Ziatech Corporation ZT 8809A, Руководство по эксплуатации

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Serial Communications (16C452)
SERIAL INTERFACE (RS-232-C/422/485)
The ZT 8809A provides two high-speed RS-232-C serial ports. These
use the same programming architecture and pin definitions as the
popular 8250 from Western Digital. The serial ports are contained
within the 16C452 Communications Element.
Serial port 1 (COM1) is dedicated for RS-232-C operation, whereas
serial port 2 (COM2) is jumper selectable between RS-232-C or
RS-422/485 operation. Serial port 2 (COM2) may also be disabled
entirely with jumper W66, for use with an external card such as a
modem card mapped into the system as COM2. Refer to Appendix A
for a description of these jumpers.
Figure 8-3 shows the block diagram of a 16C452 serial port. This
device performs serial-to-parallel conversion on data characters
received from a peripheral device or a modem and parallel-to-serial
conversion on data characters received from the STD CPU.
The STD CPU can read the complete status of the serial interface at
any time. Status information reported includes the type and condition
of the transfer operation being performed, as well as any error
conditions.
Each serial port features an on-board baud rate generator capable of
operating anywhere in the 50 to 56 Kbaud range. The baud rate is
controlled by software and is usually determined by the initialization
routine. The baud rate generator is capable of dividing the timing
reference clock (1.84 MHz) input by 1 to 65,536, to produce a 16x
clock for driving the internal transmitter logic. This 16x clock also
drives the receiver logic.
The serial interface also includes Clear-To-Send (CTS), Request-To-
Send (RTS), Data-Set-Ready (DSR), Data-Terminal-Ready (DTR),
and modem-control capability.
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