An enhanced reproduction communicator board for use with the Valiant Turtle and BBC microcomputer

Features include

• - Compatible with the Valiant Turtle BBC Micro software
• - Push buttons so the Turtle can be operated without a computer connected
• - Special 'Command Mode' allows two-byte (command parameter) pairs to be sent to the board for easy control from a PC serial terminal application.
• - DIN serial connector is the same as used on the original communicator unit – original serial cables will still work.
• - DB9 serial connector for connection to a PC's serial port, or via a USB to serial port adaptor.
• - Includes 1.5m data cable for connection to the BBC Micro's RS423 serial port
• - Wide operating voltage between 6-24V via DC jack socket (5.5x2.5mm)
• - Can be powered from the Valiant Turtle's 24V power supply, just like the original communicator unit.
• - Serial only interface for controlling one Valiant Turtle.

Description of Command Mode

When first powered on 'byte mode' is selected by default, as this would normally be used with the Valiant Turtle software. If you want to control the Turtle via a serial terminal 'command mode' can be selected by sending the two bytes below.

Byte Mode
0xFB 0xFB

Command Mode
0xFD 0xFD

Once in 'command mode' the following command bytes represent the six turtle commands, the number of steps associated with the directional commands is then specified by the second byte.

Forward
0x06 0x00 – 0xFF

Backward
0x09 0x00 - 0xFF

Left Turn
0x05 0x00 – 0xFF

Right Turn
0x0A 0x00 – 0xFF

Pen Up
0x20

Pen Down
0x10

The scale can be adjusted to increase or decrease the actual distance a single directional step represents. The default distance for a single step is 0x0A (10).

Adjust Scale
0xFC 0x01 - 0x32

Once a command has been completed the communicator board will send the command byte back to the serial terminal and toggle the RTS pin, indicating that it's ready to receive the next command byte.

Power cycling the board will restore it to its default parameters and operating mode.

The following is a simple test program in BBC BASIC using *FX commands to write bytes to the communicator board via the RS423 serial interface.

    10 REM set serial baud rate to 4800
    15 *FX8,6
    20 REM write two bytes 0xFD (253) to transmit buffer
    25 REM which sets the communicator board to command mode
    30 *FX138,2,253
    35 *FX138,2,253
    40 REM pen down
    45 *FX138,2,16
    50 REM command byte - FORWARD 
    55 *FX138,2,06 
    60 REM parameter byte - 25 STEPS 
    65 *FX138,2,25
    70 REM command byte - LEFT TURN
    75 *FX138,2,05 
    80 REM parameter byte - 90 STEPS 
    85 *FX138,2,90
    90 REM command byte - RIGHT TURN
    95 *FX138,2,10 
    100 REM parameter byte - 90 STEPS 
    105 *FX138,2,90
    110 REM command byte - BACKWARD
    115 *FX138,2,09
    120 REM parameter byte - 25 STEPS 
    125 *FX138,2,25
    130 REM pen up
    135 *FX138,2,32

Serial port configuration

4800 baud – 8 Bits – No Parity – 1 Stop Bit – RTS/CTS Flow Control

The domino DIN plug on the data cable can be oriented in either of two ways, it needs to be connected to a BBC B so that the screw in the barrel of the connector faces towards the right side of the machine. No damage will occur by connecting incorrectly, the computer simply won't be able to communicate with the communicator board.