User's Manual

3-5
The data rate is 1200 bps 5%. The data code is serial 8-bit ASCII including no parity, one
start bit and one stop bit, no flow control. The logic levels for the three-wire serial interface are as
follows.
Pin # Description IMPEDANCE LOGIC LEVEL
S Remote Data Out 470  RS232
a Remote Data In 6.8 k RS232
A Ground
3-3.1.3 Data Exchange Protocol
The RCU initiates all configuration commands and status inquiries to the transceiver using the
RS-232 data communication protocol. Configuration commands control a change of state or a
parameter of the transceiver such as AM/FM or transmit frequency. Status inquiries return
transceiver data such as internal power supply voltage levels.
Each command or inquiry results in a response from the transceiver. If the transceiver receives a
valid command, it performs the command and responds with an ACK reply to the RCU. If the
transceiver receives an inquiry that requires a data response, the data is sent first, followed by
ACK. If the transceiver receives an invalid command, it responds with a NAK reply. In the case
where the transceiver is in manual (keypad) mode and it is commanded to change to the remote
mode, it first responds with HT and then responds to further commands with ACK or NAK.
The ACK, NAK, and HT remote responses are summarized in Table 3-1.