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The RCX is programmable, microcontroller-based brick that uses byte code both internally, to run user-created programs, and as a part of a serial protocol, to communicate with a PC.
This document describes the opcodes present in the RCX byte code, and is organized into the following sections:
Please note that this not an official LEGO® document or web site. LEGO® is a trademark of the LEGO Group, which does not sponsor, authorize, or endorse this document.
In addition, note that this document describes RCX internals as the author understands them. While every effort has been made to ensure that the contents of this document are accurate, the author does not guarantee that any portion of this document is correct. The author cannot be held responsible for any consequences of the use or misuse of the information contained in this document.
This opcode reference is part of RCX Internals.
Copyright © 1998, 1999, 2001 Kekoa Proudfoot. All rights reserved.
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Several opcodes are treated differently in different contexts. These opcodes are listed more than once, with each listing tagged with one or more letters to indicate the contexts to which that particular listing applies. The tags are used as follows:
Tag Description P Request sent from PC to RCX R Reply sent from RCX to PC C Command in RCX byte code
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| Absolute value | [top] [abc] [123] |
74/7c Request/Command
byte index Destination variable index. 0..31. byte source Source type for operand. Only 0 and 2 allowed. short argument Argument for operand. Compute the absolute value of the value specified by source and argument and store the result in variable index. The absolute value of the largest negative number, -32768, is defined to be the largest positive number, 32767.
83/8b Reply
void Reply indicates success.
| Alive | [top] [abc] [123] |
10/18 Request
void Check whether or not the RCX is alive. If the PC receives a reply to this request, it assumes the RCX is alive and the connection is good.
e7/ef Reply
void Reply indicates that the RCX is alive.
| Add to variable | [top] [abc] [123] |
24/2c Request/Command
byte index Destination and first operand variable index. 0..31. byte source Source type for second operand. Only 0 and 2 allowed. short argument Argument for second operand. Add the value specified by source and argument to the value of variable index, and store the result in variable index.
d3/db Reply
void Reply indicates success.
| And variable | [top] [abc] [123] |
84/8c Request/Command
byte index Destination and first operand variable index. 0..31. byte source Source type for second operand. Only 0 and 2 allowed. short argument Argument for second operand. Compute the logical AND of the value specified by source and argument and the value of variable index, and store the result in variable index.
73/7b Reply
void Reply indicates success.
| Branch always far | [top] [abc] [123] |
72/xx Command
ubyte offset Offset for computing branch target address. ubyte extension Extension to offset. Branch to the target address specified by offset and extension.
If bit 0x80 of offset is 0, the target address computed as:
address of offset + offset + 128 × extension.Otherwise, the target address computed as:
address of offset - offset - 128 × extension + 128.
| Branch always near | [top] [abc] [123] |
27/xx Command
ubyte offset Offset for computing branch target address. Branch to the target address specified by offset.
If bit 0x80 of offset is 0, the target address computed as:
address of offset + offset.Otherwise, the target address computed as:
address of offset - offset + 128.
| Call subroutine | [top] [abc] [123] |
17/xx Command
byte subroutine Index of subroutine to call. 0..7. Call the subroutine with index subroutine. If the subroutine is not defined, do nothing.
The RCX only supports one subroutine return address per task. If one subroutine calls another subroutine, execution of all tasks stops when the original subroutine returns.
| Clear message | [top] [abc] [123] |
90/xx Command
void Clear the message buffer by setting it to zero. The message buffer stores a single byte and allows for communication between multiple RCX units.
See also: send message, set message.
| Clear sensor value | [top] [abc] [123] |
d1/d9 Request/Command
byte sensor Index of sensor to clear. 0..2. Clear the counter associated with the specified sensor by setting it to a value of zero.
26/2e Reply
void Reply indicates success.
| Clear timer | [top] [abc] [123] |
a1/a9 Request/Command
byte timer Index of timer to clear. 0..3. Clear the specified timer by setting it to a value of zero.
56/5e Reply
void Reply indicates success.
| Datalog next | [top] [abc] [123] |
62/6a Request/Command
byte source Source type for next datalog entry. Only 0, 1, 9, and 14 allowed. byte argument Argument for next datalog entry. Set the next datalog entry to the value specified by source and argument. If the datalog is full, leave it unmodified.
95/9d Reply
byte errorcode Return value. A return value of 0 indicates success, while a return value of 1 indicates that the datalog was full.
| Decrement loop counter far | [top] [abc] [123] |
92/xx Command
ushort offset Offset for computing branch target address. Decrement the current loop counter, then, if the loop counter is less than zero, pop the loop counter stack and branch to the target address specified by offset.
The branch target address is computed as:
address of first byte of offset + offset.Note that offset is unsigned. Backward branching is not allowed with this operation.
| Decrement loop counter near | [top] [abc] [123] |
37/xx Command
ubyte offset Offset for computing branch target address. Decrement the current loop counter, then, if the loop counter is less than zero, pop the loop counter stack and branch to the target address specified by offset.
The branch target address is computed as:
address of offset + offset.Note that offset is unsigned. Backward branching is not allowed with this operation.
| Delete all subroutines | [top] [abc] [123] |
70/78 Request/Command
void Delete all subroutines belonging to the current program.
87/8f Reply
void Reply indicates success.
| Delete all tasks | [top] [abc] [123] |
40/48 Request/Command
void Stop execution and delete all tasks belonging to the current program.
b7/bf Reply
void Reply indicates success.
| Delete firmware | [top] [abc] [123] |
65/6d Request/Command
byte key[5] Key. Must be {1,3,5,7,11}. If key is valid, stop execution and delete the firmware. Otherwise, do nothing. The key prevents the firmware from being accidentally erased.
Before the firmware may be replaced, it must be deleted.
92/9a Reply
void Reply indicates success.
| Delete subroutine | [top] [abc] [123] |
c1/c9 Request/Command
byte subroutine Index of subroutine to delete. 0..7. Delete the specified subroutine. If the subroutine is currently being executed, the related task is stopped.
36/3e Reply
void Reply indicates success.
| Delete task | [top] [abc] [123] |
61/69 Request/Command
byte task Index of task to delete. 0..9. Delete the specified task. If the task is currently running, execution of all tasks stops.
96/9e Reply
void Reply indicates success.
| Divide variable | [top] [abc] [123] |
44/4c Request/Command
byte index Destination and first operand variable index. 0..31. byte source Source type for second operand. Only 0 and 2 allowed. short argument Argument for second operand. Divide the value of variable index by the value specified by source and argument, and store the result in variable index. If the source and argument specify a denominator of zero, the variable index is left unchanged.
b3/bb Reply
void Reply indicates success.
| Get battery power | [top] [abc] [123] |
30/38 Request
void Request the battery voltage from the RCX.
c7/cf Reply
ushort millivolts Battery voltage. Reply indicates the current voltage of the RCX battery, in mV. A fresh set of alkaline batteries typically has a reading of around 9.3V.
| Get memory map | [top] [abc] [123] |
20/28 Request
void Request the memory map from the RCX.
d7/df Reply
ushort map[94] Memory map. Reply contains the user program memory map of the RCX. The memory map is an array of 94 16-bit big endian addresses, organized as follows:
Index Description 0-7 Starting addresses, program 0, subroutines 0-7 8-15 Starting addresses, program 1, subroutines 0-7 16-23 Starting addresses, program 2, subroutines 0-7 24-31 Starting addresses, program 3, subroutines 0-7 32-39 Starting addresses, program 4, subroutines 0-7 40-49 Starting addresses, program 0, tasks 0-9 50-59 Starting addresses, program 1, tasks 0-9 60-69 Starting addresses, program 2, tasks 0-9 70-79 Starting addresses, program 3, tasks 0-9 80-89 Starting addresses, program 4, tasks 0-9 90 First datalog address 91 Next datalog address 92 First free address 93 Last valid addesss
| Get value | [top] [abc] [123] |
12/1a Request
byte source Source type for value. Sources 2 and 4 not allowed. byte argument Argument for value. Request the value specified by source and argument.
e5/ed Reply
short value Return value. Reply contains the requested value.
| Get versions | [top] [abc] [123] |
15/1d Request
byte key[5] Key. Must be {1,3,5,7,11}. Request the ROM and firmware versions from the RCX. If key is not valid, no reply is sent.
e2/ea Reply
short rom[2] ROM version number. short firmware[2] Firmware version number. Reply contains the ROM and firmware version numbers. Each version number is composed of two big endian shorts; the first is the major version number and the second is the minor version number.
The ROM always has major and minor version numbers 3 and 1. The firmware shipped with the Robotics Invention System has major and minor version numbers 3 and 9. When no firmware is installed, both firmware version numbers are 0.
| Multiply variable | [top] [abc] [123] |
54/5c Request/Command
byte index Destination and first operand variable index. 0..31. byte source Source type for second operand. Only 0 and 2 allowed. short argument Argument for second operand. Multiply the value of variable index by the value specified by source and argument, and store the result in variable index.
a3/ab Reply
void Reply indicates success.
| Or variable | [top] [abc] [123] |
94/9c Request/Command
byte index Destination and first operand variable index. 0..31. byte source Source type for second operand. Only 0 and 2 allowed. short argument Argument for second operand. Compute the logical OR of the value specified by source and argument and the value of variable index, and store the result in variable index.
63/6b Reply
void Reply indicates success.
| Play sound | [top] [abc] [123] |
51/59 Request/Command
byte sound Sound type. 0..5. Play the specified sound.
There are six avaiable sound types:
Index Description 0 Blip 1 Beep beep 2 Downward tones 3 Upward tones 4 Low buzz 5 Fast upward tones
a6/ae Reply
void Reply indicates success.
| Play tone | [top] [abc] [123] |
23/2b Request/Command
short frequency Tone frequency. byte duration Tone duration. Play the sound specified by frequency and duration. The tone frequency is measured in Hz, and the tone duration is measured in 1/100ths of a second.
d4/dc Reply
void Reply indicates success.
| Power off | [top] [abc] [123] |
60/68 Request/Command
void Turn off the RCX. If the power down delay is zero, do nothing.
97/9f Reply
void Reply indicates success.
| Return from subroutine | [top] [abc] [123] |
f6/xx Command
void Return from subroutine. This opcode is intended to be used in the middle of a subroutine, since a return from subroutine opcode is automatically added to every subroutine that is downloaded.
| Send message | [top] [abc] [123] |
b2/xx Command
byte source Source type for message. Only 0 and 2 allowed. byte argument Argument for message. Send the value specified by source and argument to other RCX units. The value is sent by broadcasting a set message request over the infrared link.
| Set datalog size | [top] [abc] [123] |
52/5a Request/Command
short size New datalog size. Allocate and initialize a datalog with space for size data entries. A single extra entry is always allocated to hold the current size of the datalog, which is initialized to one since this size value is stored as the first entry in the datalog.
a5/ad Reply
byte errorcode Return value. A return value of 0 indicates success, while a return value of 1 indicates that there is insufficient memory to allocate a datalog of the requested size.
| Set display | [top] [abc] [123] |
33/3b Request/Command
byte source Source type for device. Only 0 and 2 allowed. short argument Argument for device. Display the input/output value associated with the device specified by source and argument. Valid devices are:
Index Description 0 Watch 1 Sensor 1 2 Sensor 2 3 Sensor 3 4 Motor A 5 Motor B 6 Motor C This operation controls the same functionality as the View button on the face of the RCX.
c4/cc Reply
void Reply indicates success.
| Set loop counter | [top] [abc] [123] |
82/xx Command
byte source Source type for counter value. Only 0, 2, and 4 allowed. byte argument Argument for counter value. Push the loop counter stack, then set the topmost loop counter to the value specified by source and argument. There are four loop counters. If more than four loops are nested, the loop counter stack is not pushed before the topmost value is set.
| Set message | [top] [abc] [123] |
f7/xx Request/Command
byte message Message value. Set the value of the message buffer to message. This is the only request with no matching reply.
| Set motor direction | [top] [abc] [123] |
e1/e9 Request/Command
byte code Bit field to specify a direction and up to three motors. Set the direction of the motors according to code. The bits of code have the following meanings:
Bit Description 0x01 Modify direction of motor A 0x02 Modify direction of motor B 0x04 Modify direction of motor C 0x40 Flip the directions of the specified motors 0x80 Set the directions of the specified motors to forward If both bit 0x40 and bit 0x80 are 0, the directions of the specified motors are set to reverse. If both bit 0x40 and bit 0x80 are 1, the directions of the specified motors are flipped.
16/1e Reply
void Reply indicates success.
| Set motor on/off | [top] [abc] [123] |
21/29 Request/Command
byte code Bit field to specify an on/off state and up to three motors. Set the on/off state of the motors according to code. The bits of code have the following meanings:
Bit Description 0x01 Modify on/off state of motor A 0x02 Modify on/off state of motor B 0x04 Modify on/off state of motor C 0x40 Turn off the specified motors 0x80 Turn on the specified motors If both bit 0x40 and bit 0x80 are 0, the specified motors are set to float, which allows the shafts of the specified motors to spin freely. Setting both bit 0x40 and bit 0x80 to 1 turns on the specified motors.
d6/de Reply
void Reply indicates success.
| Set motor power | [top] [abc] [123] |
13/1b Request/Command
byte motors Bit field to specify up to three motors. byte source Source type for power level. Only 0, 2, and 4 allowed. byte argument Argument for power level. Set the power level of the motors specified by motors to the value specified by source and argument. The bits of motors have the following meanings:
Valid power levels are between 0 and 7, inclusive. Other power levels are ignored.
Bit Description 0x01 Modify power level of motor A 0x02 Modify power level of motor B 0x04 Modify power level of motor C
e4/ec Reply
void Reply indicates success.
| Set power down delay | [top] [abc] [123] |
b1/b9 Request/Command
byte minutes Power down delay. Set the power down delay to the specified value, which is measured in minutes. A power down delay of 0 instructs the RCX to remain on indefinitely and causes the power off opcode to be ignored.
46/4e Reply
void Reply indicates success.
| Set program number | [top] [abc] [123] |
91/99 Request/Command
byte program Program number. 0..4. Stop execution and set the current program number to the specified value.
66/6e Reply
void Reply indicates success.
| Set sensor mode | [top] [abc] [123] |
42/4a Request/Command
byte sensor Index of sensor to modify. 0..2. byte code Packed sensor slope and mode. Set the slope and mode of sensor number sensor to the value specified by mode, and clear that sensor's value. The bits of mode are split into two portions. Bits 0-4 contain a slope value in 0..31, while bits 5-7 contain the mode, 0..7. The eight modes, which control the value returned by the sensor, are:
Mode Name Description 0 Raw Value in 0..1023. 1 Boolean Either 0 or 1. 2 Edge count Number of boolean transitions. 3 Pulse count Number of boolean transitions divided by two. 4 Percentage Raw value scaled to 0..100. 5 Temperature in °C 1/10ths of a degree, -19.8..69.5. 6 Temperature in °F 1/10ths of a degree, -3.6..157.1. 7 Angle 1/16ths of a rotation, represented as a signed short. The slope value controls 0/1 detection for the three boolean modes. A slope of 0 causes raw sensor values greater than 562 to cause a transition to 0 and raw sensor values less than 460 to cause a transition to 1. The hysteresis prevents bouncing between 0 and 1 near the transition point. A slope value in 1..31, inclusive, causes a transition to 0 or to 1 whenever the difference between consecutive raw sensor values exceeds the slope. Increases larger than the slope result in 0 transitions, while decreases larger than the slope result in 1 transitions. Note the inversions: high raw values correspond to a boolean 0, while low raw values correspond to a boolean 1.
b5/bd Reply
void Reply indicates success.
| Set sensor type | [top] [abc] [123] |
32/3a Request/Command
byte sensor Index of sensor to modify. 0..2. byte type Sensor type. 0..4. Set the type of sensor number sensor to type, and set the mode of that sensor to a default value. Valid types and their default modes are:
Type Description Default Mode 0 Raw Raw 1 Touch Boolean 2 Temperature Temperature in °C 3 Light Percentage 4 Rotation Angle
c5/cd Reply
void Reply indicates success.
| Set time | [top] [abc] [123] |
22/2a Request/Command
byte hours Current hour. 0..23. byte minutes Current minute. 0..59. Set the current time to hours and minutes.
d5/dd Reply
void Reply indicates success.
| Set transmitter range | [top] [abc] [123] |
31/39 Request/Command
byte range Transmitter range. 0 or 1. Set the transmitter range. 0 indicates short range, 1 indicates long range. Other values are ignored.
c6/ce Reply
void Reply indicates success.
| Set variable | [top] [abc] [123] |
14/1c Request/Command
byte index Destination and first operand variable index. 0..31. byte source Source type for second operand. All sources are allowed. short argument Argument for second operand. Set the value of variable index to the value specified by source and argument.
e3/eb Reply
void Reply indicates success.
| Sign variable | [top] [abc] [123] |
64/6c Request/Command
byte index Destination and first operand variable index. 0..31. byte source Source type for second operand. Only 0 and 2 allowed. short argument Argument for second operand. Set the value of variable index to 0 if the value specified by source and argument is equal to 0, 1 if the value specified by source and argument is positive, or -1 if the value specified by source and argument is negative.
93/9b Reply
void Reply indicates success.
| Start firmware download | [top] [abc] [123] |
75/7d Request
short address Firmware entry address. Typically 0x8000. short checksum Firmware checksum. Typically 0xc278. byte unknown Unknown or unused value. Always 0. Prepare the RCX for a firmware download starting at address 0x8000. The checksum is computed by taking the sum of all firmware bytes modulo 216. The specified address is used as the firmware entry point when the firmware is unlocked.
If firmware is already installed, this request is ignored and no response is sent.
82/8a Reply
byte errorcode Return value. A return value of 0 indicates success, while any other return value indicates failure.
| Start subroutine download | [top] [abc] [123] |
35/3d Request
byte unknown Unknown or unused value. Always 0. short subroutine Subroutine index. 0..7. short length Subroutine length. Prepare the RCX for a download of subroutine number subroutine of the current program. Space for length bytes is allocated in the memory map by moving other data as needed.
c2/ca Reply
byte errorcode Return value. A return value of 0 indicates success, a return value of 1 indicates that there is insufficient memory for a subroutine of the requested size, and a return value of 2 indicates that the subroutine index was invalid.
| Start task | [top] [abc] [123] |
71/79 Request/Command
byte task Index of task to start. 0..9. Start the specified task, or restart it if it is currently active. If the specified task is not defined, nothing happens.
86/8e Reply
void Reply indicates success.
| Start task download | [top] [abc] [123] |
25/2d Request
byte unknown Unknown or unused value. Always 0. short task Task index. 0..9. short length Task length. Prepare the RCX for a download of task number task of the current program. Space for length bytes is allocated in the memory map by moving other data as needed.
d2/da Reply
byte errorcode Return value. A return value of 0 indicates success, a return value of 1 indicates that there is insufficient memory for a task of the specified size, and a return value of 2 indicates that the task index was invalid.
| Stop all tasks | [top] [abc] [123] |
50/58 Request/Command
void Stops execution.
a7/af Reply
void Reply indicates success.
| Stop task | [top] [abc] [123] |
81/89 Request/Command
byte task Index of task to stop. 0..9. Stops execution of the specified task.
76/7e Reply
void Reply indicates success.
| Subtract from variable | [top] [abc] [123] |
34/3c Request/Command
byte index Destination and first operand variable index. 0..31. byte source Source type for second operand. Only 0 and 2 allowed. short argument Argument for second operand. Subtract the value specified by source and argument from the value of variable index, and store the result in variable index.
c3/cb Reply
void Reply indicates success.
| Test and branch far | [top] [abc] [123] |
95/xx Command
byte opsrc1 Packed operator and source type for first value. Sources 4 and 8 not allowed. byte src2 Source type for second value. Sources 2, 4, and 8 not allowed. short arg1 Argument for first value. byte arg2 Argument for second value. short offset Offset for computing branch target address. Compare two values against one another and branch if the comparison is true. Bits 0-3 of opsrc1 contain the source for the first value, while arg1 contains the argument for the first value. The second value is specified by src2 and arg2. The comparison operator, which is stored in bits 6-7 of opsrc1, has a value in 0..3. The meanings of these values are:
Value Description 0 First value less than or equal to second value 1 First value greater than or equal to second value 2 First value not equal to second value 3 First value equal to second value The branch target address is computed as:
address of first byte of offset + offset.Note that offset is signed. Backward branching is allowed with this operation.
| Test and branch near | [top] [abc] [123] |
85/xx Command
byte opsrc1 Packed operator and source type for first value. Sources 4 and 8 not allowed. byte src2 Source type for second value. Sources 2, 4, and 8 not allowed. short arg1 Argument for first value. byte arg2 Argument for second value. byte offset Offset for computing branch target address. Compare two values against one another and branch if the comparison is true. Bits 0-3 of opsrc1 contain the source for the first value, while arg1 contains the argument for the first value. The second value is specified by src2 and arg2. The comparison operator, which is stored in bits 6-7 of opsrc1, has a value in 0..3. The meanings of these values are:
Value Description 0 First value less than or equal to second value 1 First value greater than or equal to second value 2 First value not equal to second value 3 First value equal to second value The branch target address is computed as:
address of first byte of offset + offset.The value of offset is unsigned. Backward branching is not allowed with this operation. Use test and branch far to test and branch backward.
| Transfer data | [top] [abc] [123] |
45/4d Request
short index Sequence number of data block. short length Length of data block. byte data[length] Data block. byte checksum Checksum of data block. Download block number index, containing length data bytes, to the RCX. The bytes are stored as required by the most recent start firmware download, start subroutine download, or start task download operation.
Block sequence numbers start at 1 and increase by one with each successive block transferred. The special sequence number 0 indicates the last block of a transfer. Once this sequence number is received by the RCX, another start download operation is required before additional data blocks may be transferred.
The checksum is computed by taking the sum of all bytes in the data block modulo 256. It is only checked for packets that have a non-zero sequence number.
Note that, for task and subroutine downloads, the RCX does not check that the total number of bytes sent was equal to the amount of space allocated by the corresponding start download operation. If too few bytes are sent, a portion of the downloaded task or subroutine will contain invalid code; if too many bytes are sent, other tasks and subroutines may become corrupted.
b2/ba Reply
byte errorcode Return value. A return value of 0 indicates success, a return value of 3 indicates a block checksum failure, a return value of 4 indicates a firmware checksum error, and a return value of 6 indicates an invalid or missing download start. If the block sequence number is out of order, no reply is sent.
When block checksum error number 3 is received, the PC may either retransmit the erroneous block or restart the download. A block with index 0 cannot be retransmitted. Moreover, a bug in the ROM requires that the PC increment its block sequence number when retransmitting firmware data in response to a block checksum error.
During a firmware download, duplicate transfer data requests are handled incorrectly. If the PC does not receive a transfer data reply, block sequence numbers might get out of sync.
| Unlock firmware | [top] [abc] [123] |
a5/ad Request
byte key[5] Key. Must be {76,69,71,79,174} = {"LEGO®"}. Activate the firmware after a successful download.
52/5a Reply
byte data[25] Return value. Always {"Just a bit off the block!"}. Reply indicates success.
| Upload datalog | [top] [abc] [123] |
a4/ac Request
short first Index of first entry to upload. short count Number of entries to upload. Upload count datalog entries, starting with entry number first.
The datalog entry with index 0 always contains the current size of the datalog, which is guaranteed to be at least one since the current size entry is considered to be part of the datalog. After the current size entry are size data entries, where size is specified with the set datalog size operation and is initially zero.
It is an error to read an entry outside the valid range of the datalog.
53/5b Reply
dlrec data[length] Requested datalog entries. Reply contains the requested datalog entries, stored as an array of length dlrec duples, where length was specified as the count in the corresponding request. Each dlrec is organized as follows:
byte type Type of datalog entry. short value Value of datalog entry. The type of each dlrec specifies the appropriate interpretation of the corresponding value. Valid types are:
Type Description 0xff Current datalog size 0x00-0x1f Variable value (source 0, variables 0..31) 0x20-0x23 Timer value (source 1, timers 0..3) 0x40-0x42 Sensor reading (source 9, sensors 0..2) 0x80 Clock reading (source 14) If an error occurs while reading the datalog, length is set to zero.
| Wait | [top] [abc] [123] |
43/xx Command
byte source Source type for delay. Only 0, 2, and 4 allowed. short argument Argument for delay. Wait for the delay specified by source and argument. The delay is in 1/100ths of a second.
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This section describes the available sources and arguments.
Sources are like addressing modes. They specify where and how to get certain operand values.
There are 16 sources available, of which 13 apply to the RCX:
Motor state is encoded as a single byte. Bits 0-2 contain the motor power, 0..7. The remaining bits are used as follows:
Source Name Argument Description 0 Variable Variable index, 0..31. Returns value of specified variable. 1 Timer Timer index, 0..3. Returns value of specified timer, in 1/100ths of a second. 2 Immediate Immediate value. Returns specified immediate value. 3 Motor State Motor index, 0..2. Returns state of specified motor. See below. 4 Random Maximum value. Returns random value, 0..max. 5 Reserved N/A Cybermaster only. 6 Reserved N/A Cybermaster only. 7 Reserved N/A Cybermaster only. 8 Current Program Ignored. Returns current program number. 9 Sensor Value Sensor index, 0..2. Returns value of specified sensor. 10 Sensor Type Sensor index, 0..2. Returns type of specified sensor. 11 Sensor Mode Sensor index, 0..2. Returns mode of specified sensor. 12 Raw Sensor Value Sensor index, 0..2. Returns raw value of specified sensor, 0..1023. 13 Boolean Sensor Value Sensor index, 0..2. Returns boolean value of specified sensor, 0..1. 14 Clock Must be 0. Returns minutes since power on. 15 Message Must be 0. Returns value of message buffer.
If both bit 0x40 and bit 0x80 are 0, the specified motor is set to float.
Bit Description Notes 0x08 Forward flag 0 if forward, 1 if reverse. 0x40 Off flag 1 if off. 0x80 On flag 1 if on.
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Several people contributed information which helped to make this document more complete and accurate:
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There are several known issues and missing items as of Sat May 8 1999:
A few of these items are currently addressed in the Serial Protocol section of RCX Internals.
If you are interested in trying out the protocol, you might be interested in the Send program, which allows you to send opcodes to the RCX.
| Copyright © 1998, 1999 Kekoa Proudfoot. All rights reserved. | kekoa@graphics.stanford.edu |