Measurement Computing CIO-RELAY08 - Manual (Page 9)

4 PROGRAMMING
The CIO-RELAY boards are easy to program. From one to four eight-bit registers
are written to control relays or can be read to determine the state of relays.
In addition to direct I/O programming, the boards are f ully supported by the
powerful Universal Library program as well as most third-party application
programs.
4.1 DIRECT I/O REGISTER PROGRAMMING
The CIO-RELAY family uses between one and four I/O addresses. Each address
controls eight relay s. Relays are co ntrolled by writing to these register(s). T he
address map of the CIO-RELAY boards is shown below.
BASE ADDRESS Relays 0-7 Read/Write (All CIO-RELAY boards
BASE + 1 Relays 8-15 Read/Write (CIO-RELAY16, -24, -32)
BASE + 2 Relays 16-23 Read/Write (CIO-RELAY24, -32)
BASE + 3 Relays 24-31 Read/Write (CIO-RELAY32 only)
The registers are written to and read from as a single, 8-bit byte. Each bit controls an
output to a relay (write) or represents the state of a relay (read).
All registers are read left to right. The leftmost bit (the eighth bit) being the most
significant bit. Following this format, bit seven (OP7) of BASE + 0 corresponds to
relay number 7 and bit 0 to relay number 0.
To construct a control word, use Table 4.1 for bit weights.
Table 4-1. Bit Weights
80 128 7
40 64 6
20 32 5
10 16 4
8 8 3
4 4 2
2 2 1
1 1 0
HEX VALUE DECIMAL VALUE BIT POSITION
For example, to assemble the control byte that will turn on relays 0, 1, 3, 5, and 7,
we see in Table 4-2 that we need to write HEX AB or decimal 171.
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