Real Time Devices AD1200 User Manual page 36

Mode 4
Software-Triggered Strobe
Mode 5 Hardware Triggered Strobe (Retriggerable)
These modes are detailed in *re 8254 Data Sheet, reprinted from Intel in Appendix C.
Digital VO, Programmable Peripheral Interface
The programmable peripheral interface @PI) is used for digital VO functions. This high-performanceTlLl
CMOS compatible chip has 24 digital I/O lines divided into two goups of 12 lines each:
Group A - Port A (8 lines) and Port C Upper (4 lines);
Group B ---- Port B (8 lines) and Port C Lower (4 lines).
Port A and Port C are available at the external I/O connector, p2. port B is dedicated to on-board functions and
is not available for your use. You can use the 16 lines of Ports A and C in one of these three PPI operating modes:
Mode 0 - Basic input/output. Lets you use simple input and output operation for a porL Data is written to or
read from the specified port.
Mode I - Strobed input/output. I-es you transfer IIO data from Port A in conjunction wittr strobes or hand-
shaking signals.
Mode 2 - Strobed bidirectional input/output. I*ts you communicate bidirectionally wittr an external device
through Port A. Handshaking is similar to Mode 1.
These modes are detailed in the 8255 Data Sheet, reprinted from Intel in Appendix C.
Interrupts
The 1200 has four jumper-selectable intemrpt sources: end-of-convert, DMA done, the external trigger, and the
output of timer/counter 2. The end-of+onvert signal can be used to interrupt the computer when an A/D convenion
is completed. The DMA done is used in the DMA mode to generate an intemtpt whenever a DMA transfer is
completed. The external trigger at the VO connector can be used to generate an intemrpt whenever the nigger line
changes states from low to high. Or, the output of timer/counter 2 cangenerate an intemrpt whenever rhe count
reaches 0. Chapter 1 tells you how to set the jumpers on the intemrpt header connector P7, and Chapter 4 describes
how to program intemrpts.
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