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10. PARALLEL I/O
The ZT 8904 includes six 8-bit parallel ports for a total of 48 I/O signals. Three of the
parallel ports are available to the application through frontplane connector J4. The
remaining three parallel ports are dedicated to controlling and 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 explained in Chapter 11,
"
System Registers
."
Each of the 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
•
Software programmable input debounce
•
Stable outputs during power up and reset
•
Continuous data transfer rates up to 1 Mbyte/second
•
Software programmable event sense interrupt generation
•
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
FUNCTIONAL DESCRIPTION
The parallel I/O signals are supported through the 16C50A, a custom ASIC device
designed by Ziatech. Refer to Appendix C, "
PIA System Setup Considerations
," for tips
on preventing latchup from the CMOS parts in the 16C50A.
A functional diagram of each I/O signal is illustrated in the following figure. The diagram
includes an output latch, an output buffer, and an input buffer. These functional blocks
are described in the following topics.