B-2
Computer Group Literature Center Web Site
Serial Interconnections
B
synchronous (SDLC/HDLC) and asynchronous protocols. The hardware
supports asynchronous serial baud rates of 110B/s to 38.4KB/s and
synchronous baud rates of up to 2.5MB/s.
Each port supports the CTS, DCD, RTS, and DTR control signals, as well
as the TxD and RxD transmit/receive data signals and TxC/RxC
synchronous clock signals. Since not all modem control lines are available
in the Z85230, a Z8536 CIO device is used to provide the missing modem
lines.
EIA-232-D Connections
The EIA-232-D standard defines the electrical and mechanical aspects of
this serial interface. The interface employs unbalanced (single-ended)
signaling and is generally used with DB-25 connectors, although other
connector styles (for example, DB-9 and RJ-45) are sometimes used as
well.
Table B-1
lists the standard EIA-232-D interconnections. Not all pins
listed in the table are necessary in every application.
To interpret the information correctly, remember that the EIA-232-D serial
interface was developed to connect a terminal to a modem. Serial data
leaves the sending device on a Transmit Data (TxD) line and arrives at the
receiving device on a Receive Data (RxD) line. When computing
equipment is interconnected without modems, one of the units must be
configured as a terminal (data terminal equipment: DTE) and the other as
a modem (data circuit-terminating equipment: DCE). Since computers are
normally configured to work with terminals, they are said to be configured
as a modem in most cases.