Measurement Computing PCIe-DIO96H - Manual (Page 13)

13
Chapter 3
Functional Details
CIO-ERB24 and SSR-RACK24 daisy chain configuration
Many relay and solid-state relay (SSR) racks provide only 24-bits of digital I/O. You can configure the CIO-
ERB24 relay output board and SSR-RACK24 I/O module rack in a daisy chain configuration to use all of the
digital I/O bits provided by the PCIe-DIO96H board. An example of the daisy chain configuration scheme for
each board is shown below.
The PCIe-DIO96H board provides digital I/O in a group of 96 bits. Each of the C100FF-x cable's 50-pin
connectors provides 48 bits. To use all of the board's 96 digital I/O bits to control relays and/or SSRs, configure
the daisy chain as shown in Figure 4.
CIO-ERB24
or
SSR-Rack24 IN
OUT
CIO-ERB24
or
SSR-Rack24 IN
OUT
CIO-ERB24
or
SSR-Rack24 IN
OUT
CIO-ERB24
or
SSR-Rack24 IN
OUT
C100FF-x Cable
P
C
Ie
-D
IO
9
6
H
Figure 4. PCIe-DIO96H to C100FF-x to relay rack daisy chain cabling
The 24 digital I/O bits on pins 1-24 control the first relay board on the chain. The 24 digital I/O bits on pins
25-50 control the second relay/SSR board on the daisy chain and so on, for up to 100 pins.
82C55 emulation (mode 0)
The PCIe-DIO96H emulates the 82C55 chip (mode 0). The 82C55 emulation 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
output, it could be turned on or off every time the board is reset.
To establish a consistent TTL level at power-up, configure each port resistor with InstaCal for either pull-up or
pull-down.
Whenever an 82C55 emulation is powered on or reset, all pins are set to high-impedance input. Based on
standard TTL functionality, these inputs typically float high, and may have enough drive current to turn on
external devices. Consequently, if you have output devices such as solid state relays, they may be switched on
whenever the computer is powered on or reset. To prevent unwanted switching, and to drive all outputs to a
known state after power on or reset, configure each port resistor with InstaCal.
Unconnected inputs are forced to the pull direction
Unconnected inputs will float in the pull direction that is configured for the port with InstaCal (either up/high or
down/low).