Measurement Computing PC104-DAS08 - Manual (Page 12)

3 REGISTER ARCHITECTURE
3.1 CONTROL & DATA REGISTERS
The PC104-DAS08 is controlled and monitored by writing to and reading from eight
consecutive 8-bit I/O addresses. The first address, or BASE ADDRESS, is
determined by setting a bank of switches on the board.
Most often, register manipulation is best left to experienced programmers as most of
the PC104-DAS08 possible functions are implemented in easy to use Universal
Library functions.
The register descriptions follow the format:
CH1 CH2 CH4 CH8 A/D12
LSB
A/D11 A/D10 A/D9
0 1 2 3 4 5 6 7
Numbers along the top row are the bit positions within the 8-bit byte and the
numbers and symbols in the bottom row are the functions associated with that bit.
To write to or read from a register in decimal or HEX, the weights in Table 3-1
apply:
Table 3-1. 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
To write control words or data to a register, the individual bits must be set to 0 or 1
then combined to form a byte.
The method of programming required to set/read bits from bytes is beyond the scope
of this manual.
In summary form, the registers and their function are listed on Table 4-2. Within
each register are eight bits which either constitute a byte of data or eight individual
bit set/read functions.
8