CCC Serial Interface

Introduction

This is a protocol to interface RS232 to an A6 D8 bus SLOWLY! It is designed to be as lightweight as possible, so no extra commands etc will be added.

Serial Port Settings

• 115200 BAUD, no parity, 1 stop bit, no flow control.

NOTE, the BAUD rate is derived from the clock, so using an external clock with a different frequency will change the BAUD rate!

Protocol

• Data arranged in 2 byte messages: 1 byte op-code, 1 byte data
• A message sent always generates a message reply : But keep in mind a message sent could reset the board and hence will not generate a reply
• No timeouts, but no error conditions either. A command works, or it doesn't, this code does not care.

Message Format

Bit	Description
Byte 0
7	0= Message, 1= Reply. All messages acknowledge with a reply
6	Write/(not Read) to register
5:0	Address of register
Byte 1
7:0	Byte of data for writing, reply contains data read

TX Message

	Bit
Byte	7	6	5	4	3	2	1	0
0	0	WR/nRD	0	0	ADDR (3:0)
1	DATA(7:0)

RX Message

	Bit
Byte	7	6	5	4	3	2	1	0
0	1	Same as TX Message
1	Data (as read, as sent or ack-code)

e.g.

For a TX of   0x00,0x00 (TX, Read, 2b00, Addr=0, Data = [don't care])
We see RX of  0x80,0xA1 (RX, Read, 2b00, Addr=0, Data = 0xA1)

TX=0x49,0x45 (TX, Write, 2b00, Addr=9, Data = 0x45)
RX=0xC9,0xFF (RX, Write, 2b00 Addr=9, Data = 0xFF)

Test Software

Some Python code was used to test the system is attached. [Note: the .txt at the end of the filename should be removed]. It uses a serial library from pyserial.sourceforge.net.

Change Log:

17/11/08	This doc re-born from the ashes of SerIFace (serial interface for CERC)
22/01/09	Wikirisation! Document moved here (from ~warren/ccc/docs/SerialInterface.txt)
03/04/09	Updated register list to reflect current firmware
06/04/09	Reduced address space to 4 bit
07/04/09	Moved register list to CCCRegisterList
09/12/09	Added Python test code

-- MattWarren - 22 Jan 2009