DM5210 analog input module 3-4 RTD Embedded Technologies, Inc.
Timer/Counters
An 8254 programmable interval timer provides three 16-bit, 8 MHz timer/counters to support a wide range of
timing and counting functions. These timer/counters can be cascaded or used individually for many applications.
Each timer/counter has two inputs, CLK in and GATE in, and one output, timer/counter OUT. The clock sources
for the timer/counters can be selected using jumpers on header connector P4 (see Chapter 1). The timer/counters can
be programmed as binary or BCD down counters by writing the appropriate data to the command word, as described
in Chapter 4. The command word also lets you set up the mode of operation. The six programmable modes are:
Mode 0
Event Counter (Interrupt on Terminal Count)
Mode 1
Hardware-Retriggerable One-Shot
Mode 2
Rate Generator
Mode 3
Square Wave Mode
Mode 4
Software-Triggered Strobe
Mode 5
Hardware Triggered Strobe (Retriggerable)
These modes are detailed in the 8254 Data Sheet, reprinted from Intel in Appendix C.
Digital I/O, Programmable Peripheral Interface
The 8255 programmable peripheral interface (PPI) is used for digital I/O functions. This high-performance TTL/
CMOS compatible chip has 24 digital I/O lines divided into two groups 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).
Sixteen lines, Port A, Port C Lower, and Port C Upper, are brought out to the I/O connector. Four of Port B’s
lines are used to control on-board functions. The remaining four Port B lines, PB4-PB7, are available at the pads
labeled P8 on the module. You can use these ports in one of these three PPI operating modes:
Mode 0 — Basic input/output. Lets you use simple input and output operation for a port. Data is written to or
read from the specified port.
Mode 1 — Strobed input/output. Lets you transfer I/O data from Port A in conjunction with strobes or hand-
shaking signals.
Mode 2 — Strobed bidirectional input/output. Lets you communicate bidirectionally with 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 210/5210 has three jumper-selectable interrupt sources: end-of-convert, 8254 timer/counter output 2, and
the external clock for timer/counter 2 brought onto the module through P2. The end-of-convert signal can be used to
interrupt the computer when an A/D conversion is completed. The 8254 timer/counter output 2 can be used to
generate an end-of-count interrupt. The external clock 2 interrupt can be used to generate interrupts at any desired
interval. Chapter 4 provides some programming information about interrupts.
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