4.5Digital Input and Output

To program digital I/O operation is fairly straightforward. The digital input operation is just to read data from the corresponding registers, and the digital output operation is to write data to the corresponding registers. The digital I/O registers‘ format is shown in section 3.14. Note that the DIO data channel can only be read or written in form of 16 bits together. It is impossible to access individual bit channel.

The PCI-9111 provides 16 digital input and 16 digital output channels through the connector CN1 and CN2 on board. The digital I/O signal is fully TTL/DTL compatible. The detailed digital I/O signal specification can be referred to section 1.3.

74LS244

Digital Input(DI)

 

From TTL Signal

 

Digital Output (DO)

74LS373

To TTL Devices

Digital GND (DGND)

 

PCI-9111

Outside Device

4.6Timer/Counter Operation

4.6.1Introduction

One 8254 programmable interval timer/counter chip is installed on PCI-9111. There are three counters in one 8254 chip and 6 possible operation modes for each counter. The block diagram of the timer/counter system is shown in following diagram.

 

 

 

 

 

AD Trigger Signal

8254 Chip

 

 

 

 

Pre-Trigger

 

 

 

C

 

 

 

 

 

 

 

 

 

Counter #0

O

 

 

 

Signal

Pre-Trigger

Gate Control

 

 

 

 

 

Control

 

 

 

G

 

 

 

 

(Pin-12 of CN3)

 

 

 

 

 

 

 

 

 

 

 

 

C

 

Internal Timer Pacer

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Timer #1

O

 

 

 

 

 

 

 

 

 

 

 

 

Internal 2 MHz Clock

'H'

G

 

 

 

 

 

 

 

C

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Timer #2

O

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

'H'

G

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figure 4.6.1 Timer/Counter System of PCI-9111

34 ∙ Operation Theorem