Manual

1
Serial Protocol for the STn00 and SRn00 devices
Issue 2
Date 5/6/00
1 Introduction
This document describes the serial protocol for re-programming the STn00
and SRn00 range of transmitter and receiver modules.
There is an important difference between the VHF and the UHF products
which concerns the Intermediate Frequency (IF) used.
To differentiate between the ST and SR each has a unique product code.
For the SRn00 this is 0F6 hex and for STn00 it is 0F5 hex.
2 Data Format
Two baud rates are used for differing functions. Throughout this document,
which one is being used is given. The two baud rates are:
Baud rate 19,200, 8 data bits, 1 start bit, 1 stop bit, no parity
Baud rate 1,200, 8 data bits, 1 start bit, 1 stop bit, no parity
The internal PIC is running an RC clock which can vary considerable with
component tolerance and temperature. To overcome this, a serial protocol is
used which looks a the input waveform from the PC as a pulse, the duration
of which determines whether the input data is a binary 1 or 0. If the baud rate
is 19,200, the data byte to be transmitted to the radio is as follows:
0 (decimal) = binary 0
255 (decimal) = binary 1
During readback the data can vary and so must be interpreted as follows:
Value < 241 (dec) = binary 0
Value $ 241 (dec) = binary 1
For the one data byte, 8 bytes must be sent representing each bit.
If the baud rate is 1,200, then the data sent is a normal 8 bit byte.
Note: throughout the document the value of the data is given assuming an
RS232 interface. If TTL or similar logic levels are used then the data
must be inverted.