Measurement-computing PC104-PDISO8 Manual de usuario descargar pdf (Pagina 9)

3 REGISTER DESCRIPTIONS

3.1 INTRODUCTION

Two, eight-bit registers located at the base address (relay output) and base + 1

(isolated inputs) are read or written to for control of relays, read back the state of

relays or sense inputs (Table 3-1).

Table 3-1. Board Registers

Not UsedBASE + 3

Not UsedBASE + 2

Read OnlyIsolated InputsBASE + 1

Relay OutputsBASE + 0

READ/WRITERELAY OUTPUTBASE ADDRESS

Although the PC104-PDISO8 decodes up to four addresses, two of those are not used.

This conforms to the design of the original PDISO-8, of which the PC104-PDISO8 is

a true clone.

Please use the Universal Library if you are programming from a high level language.

The registers are written to and read from as a single 8-bit byte. Each bit controls an

output or represents the state of an input.

Both registers are read left to right. The leftmost bit being the most significant bit.

Following this format, bit 7 of BASE + 0 corresponds to relay 7 and bit 0 to relay 0.

To construct a control word, refer to Table 3-2 for bit weights.

Table 3-2. Bit Weights

801287

40646

20325

10164

883

442

221

110

HEX VALUEDECIMAL VALUEBIT POSITION

Example: To assemble a control byte with relays 0, 1, 3, 5, and 7 turned ON , refer to

Table 3-3 for the coding.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 ... 19 20

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Measurement-computing PC104-PDISO8 Manual de usuario Pagina 9