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Theory of Operation
Chapter 3
Data Transceivers
The data transceivers control the sending and receiving of data to and from the PC I/O Channel.
PC I/O Channel Control Circuitry
The base address used by the board is determined by an onboard switch setting. The address on
the PC I/O channel bus is monitored by the address decoder, which is part of the I/O channel
control circuitry. If the address on the bus matches the selected I/O base address of the board,
the board is enabled and the corresponding register on the PC-TIO-10 is accessed.
In addition, the I/O channel control circuitry monitors and transmits the PC I/O channel control
and support signals. The control signals identify transfers as read or write, memory or I/O, and
8-bit, 16-bit, or 32-bit transfers. The PC-TIO-10 uses only 8-bit transfers.
Am9513A System Timing Controller
The Am9513A STCs are the heart of the PC-TIO-10. These chips have five individually-
controlled 16-bit counters, each of which can be configured to operate in a number of different
modes. Therefore, the PC-TIO-10 can be used for applications such as rate generation, FSK, and
pulse parameter measurement. Each of the counters has its own source (SOURCE), gate
(GATE), and output (OUT) connections. Each STC has an independently-controlled, frequency-
scaler output. The STCs are clocked by an onboard 1-MHz crystal oscillator to give 1-µsec
timing resolution. In addition, SOURCE5 and SOURCE10 are clocked at 5 MHz to give 200-
nsec resolution on all timing channels. Refer to Chapter 4, Programming, or to Appendix C,
AMD Am9513A Data Sheet, for more detailed information.
MC6821 Peripheral Interface Adapter
The MC6821 PIA features sixteen bits of bit-configurable digital I/O. In addition, this device
has two edge-programmable interrupt inputs, with which the PC-TIO-10 can receive external
interrupts. Refer to Chapter 4, Programming, or to Appendix D, Motorola MC6821 Data Sheet,
for more detailed information.
Interrupt Control Circuitry
The interrupt level used by the PC-TIO-10 is selected by the onboard jumper W1. Interrupts can
be generated from two different sources, EXTIRQ1 and EXTIRQ2, each of which has
programmable-edge polarity and individual enable, clear, and disable commands. A second set
of jumpers, W2, locally connects two of the counter outputs to the interrupt circuitry. With these
connections, external wrap-backs are unnecessary if you want to use a counter to generate timed
interrupts. Refer to Chapter 4, Programming, or to Appendix D, Motorola MC6821 Data Sheet,
for more detailed information on controlling interrupts. Refer to Chapter 2, Configuration and
Installation, for more information on configuring the jumper settings.
PC-TIO-10 User Manual
3-2
© National Instruments Corporation
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