ÛZIATECH
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10. PARALLEL I/O
The ZT 8907 includes six 8-bit parallel ports for a total of 48 I/O signals. Three of the
8-bit ports are available to the user through connector J5. The remaining three parallel
ports are dedicated to controlling an monitoring local operations. The general operation
of the six parallel ports is explained in this chapter. The specific features managed by
the dedicated ports are presented in the register drawings in "
Chapter 11.
Each of the 25 parallel I/O signals is configured as an input or an output with readback
under software control. The major features of the parallel I/O are listed below.
•
12 mA sink current
•
Stable outputs during power up and reset
•
Continuous data transfer rates up to 1 Mbyte/second
•
Each I/O signal is independently programmable as an input or an output with
readback
•
Optional cable for direct connection to industry-standard I/O module mounting racks
•
Event sensing and debouncing on all ports under software control
FUNCTIONAL DESCRIPTION
The parallel I/O signals are supported through the 16C50A Digital I/O ASIC, a custom
ASIC device designed by Ziatech.
The 16C50A Digital I/O ASIC supports standard and enhanced operating modes.
Standard mode is not available to ZT 8907 users; enhanced operating mode is
automatically configured by the ZT 8907 BIOS. There are three register banks (see the
"
" topic later in this chapter) used for controlling the device's
features. These register banks are selected by programming bits 6 and 7 of I/O port E7h
with a "00" for bank 0, and a "01" for bank 1, and a "10" for bank 2.
The "
Parallel Port Functional Diagram
" on the following page shows the internal circuitry
of each I/O signal. The diagram includes an output latch, an output buffer, and an input
buffer. These functional blocks are described in the following topics.
Refer to Appendix C, "
Digital I/O ASIC System Setup Considerations
," for tips on
preventing latchup from the CMOS parts in the 16C50A Digital I/O ASIC.
