Measurement-computing CIO-DIO192 Manuel d'utilisateur télécharger pdf (Page 13)

Chapter 3

Functional Details

Signal level control

The digital I/O bits on the CIO-DIO192 are 8255 CMOS TTL. The 82C55 digital I/O chip initializes all ports

as inputs on power- up and reset. A TTL input is a high impedance input. If you connect another TTL input

device to the 82C55 it could be turned ON or OFF every time the 82C55 is reset. Remember, the 82C55 is reset

to the INPUT mode.

All I/O bits are set to input mode on power up and reset. If you are using the board to control items that must be

OFF on reset, install pull-down resistors. The CIO-DIO192 has open locations where you can install Single

Inline Packages (SIP) resistor networks in either pull-up or pull-down configurations.

You can install pull-up and pull-down resistor SIP packs at each port. The positions are labeled

RNn on the

board. When installed, the SIP establishes either a high or low logic level at each of the I/O lines on the port.

To safeguard against unwanted signal levels, the devices being controlled by the CIO-DIO192 board should be

tied low or high as required by a 2.2K Ω resistor. In a 2.2K eight-resistor SIP pack, one side of all of the

resistors is connected to a single common point and brought out to a pin. The common line, usually marked

with a dot or line, is at one end of the SIP. The remaining resistor ends are brought out to the other eight pins

(refer to Figure 6).

2.2KOhm SIP

Dot indicates the

common line

(LO or HI)

I/O Lines

Figure 6. Eight-resistor SIP schematic

Figure 7

Figure 7. Pull-up and pull-down resistor SIPs schematic

shows a schematic of an SIP installed in both the pull-up and pull-down positions. Each port provides

10 holes in a line. The end labeled

HI connects to +5V. The end marked LO connects to GND. The eight holes

in the middle (n0 –n7) connect to the eight lines of the Port, A, B or C.

2.2 K SIP installed for pull-up

2.2 K SIP

Dot

+5 VDC

(GND)

User Connector

Digital I/O Lines

COM

Digital

I/O

Port

n = A, B, or C

2.2 K SIP

Dot

+5 VDC

(GND)

User Connector

Digital I/O Lines

COM

2.2 K SIP installed for pull-down

Digital

I/O

Port

n = A, B, or C

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 19 20

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Measurement-computing CIO-DIO192 Manuel d'utilisateur Page 13

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