Manual

RS-232C Communications 5-1
5 RS-232C Communications
The RS-232C Interface
The Automove System is connected to the host computer via an RS-232C/CCITT V.24
serial interface, herein referred to simply as RS-232C. The cable should be fitted with the
standard male 25-pin type "D" subminiature CINCH DBC-25P connector or equivalent.
The Automove System functions as a DTE (Data Terminal Equipment) on RS-232C. It
transmits data on pin 2 (Transmitted Data) and receives it on pin 3 (Received Data). The
Automove System always drives pin 4 (Request To Send) to the High state. With special
factory modification, pin 5 (Clear To Send) can be used to temporarily inhibit the Automove
System from transmitting characters to the host. Pin 7 is Signal Ground. Pin 20 (Data
Terminal Ready, or DTR) is used in conjunction with the Hardwired DTR handshake (if
enabled -- see below).
If the Hardwired DTR handshake is explicitly disabled, the Automove System continuously
drives pin 20 to the High state.
The Automove System can be told to temporarily ignore incoming data on pin 3; see the
ESC.) and ESC.( commands in Chapter 6.
Baud Rate
In general, the baud rate should be set to 9600 unless a lower rate is dictated by host
hardware or software limitations, long cable length, or electrical noise considerations. See
Appendix E Speed Considerations. The speed at which the host can receive and process
incoming data from the Automove System should not be a limiting consideration here, as the
Automove System can be instructed to delay and slow down its transmissions to the host.
See
ESC.M and ESC.N in Chapter 6.
Character Format
The host computer sends ACL commands and escape sequences to the Automove System as
ASCII characters. Each character should be sent with a start bit, 7 data bits, an optional
parity bit as established by the backpanel switches (see the Automove Operation Manual),
and one or two stop bits. Slightly higher throughput will result if only one stop bit is sent. It
is recommended that a parity bit always be used, because there is no other mechanism for
detecting transmission errors.
When a parity, framing, or overrun error is detected in received data, a communications error
is logged (see
ESC.E) and a "?" is sent to the host, but the incoming character is used
anyway, as received. Thus if the host is sending the wrong parity the Automove System logs
one error but works correctly. (Subsequent communications errors will not be logged.
Again, see the
ESC.E command.)