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8. SERIAL CONTROLLER
This chapter discusses operation of the four ZT 8904 serial ports. It provides
descriptions of the two software-configurable serial port registers included on the
ZT 8904.
ZT 8904 SPECIFICS
The ZT 8904 includes four serial ports: two serial ports (COM1 and COM2) compatible
with the 16450/8250, and two serial ports (COM3 and COM4) compatible with the
16550. The ZT 8903 includes only two serial ports, COM1 and COM2. The serial ports
are implemented with a 5 V charge pump technology to eliminate the need for a ±12 V
supply.
The serial ports include a complete set of handshaking and modem control signals,
maskable interrupt generation, and data transfer rates up to 115 Kbaud. Two of the
serial ports are software configured for either RS-232 or RS-485 operation. Several
choices of RS-485 control are available.
The major features of each serial port are listed below.
•
Two RS-232 channels
•
Two RS-232 or RS-485 channels (ZT 8904 and ZT 89CT04 only)
•
Does not require ±12 V
•
Baud rates up to 115 Kbaud
•
Polled and interrupt operation
•
Loopback diagnostics
Architectural differences between the four serial ports on the ZT 8904 and the COM1-
COM4 serial ports found in a standard PC architecture are discussed in the following
topics.
