8. Serial Controller
77
RS-485 Operation
Two of the serial channels, COM1 and COM2, are software programmable for RS-232
or RS-485 operation. The RS-485 functionality is not available on the ZT 8903. The
software selection is made through bits 2 and 3 of
System Register 2
. The RS-485
architecture is shown below.
Signal
Condition
+
RxD
Signal
Condition
J1-73
W28
W29
System Register 2
Bit 2
TxD
DTR
J1-72
J1-75
J1-74
W13
W12
COM1 RS-485 Architecture
Signal
Condition
+
RxD
Signal
Condition
J1-78
W30
W31
System Register 2
Bit 3
TxD
DTR
J1-77
J1-80
J1-79
W15
W14
COM2 RS-485 Architecture
Serial Channel Interface
The serial ports are configured as DTE and are available through the 80-pin frontplane
connector (J1). Optional cables convert the serial port interface to standard 9-pin D-
shell connectors. The ZT 90200 cable provides the serial interface for the ZT 8904 and
ZT 89CT04. The ZT 90203 provides the serial interface for the ZT 8903. The J1
connector pin assignments are given in the "
J1 Peripheral Pinout
" table in Appendix B.
