Measurement Computing PC104-DIO48 - Manual (Page 18)

The board is equipped with positions for pull-up/down resistors Single
Inline Packages (SIPs). The positions are marked RN1 through RN6 and
are located beside the 82C55s.
A 2.2K ohm, 8-resistor SIP is made of eight, 2.2K resistors. One side of
each resistor are all connected to a common point. The other ends go to
eight SIP pins. The common line, at one end of the SIP, is marked with a
dot or a line.
The SIP may be installed as pull-up or pull-down. At each location,
RN1 - RN6, there are 10 holes in a line. One end of the line is marked
“HI”, the other end is marked “LO”. The eight holes in the middle are
connected to the eight lines of a port, A, B, or C. To ‘pull up’ the digital
lines for a particular port, install the SIP resistor with the marked end
toward the ‘HI’ label. To pull down the digital lines for a particular
port, install the SIP resistor with the marked end toward the ‘LO’ label.
Install and solder the SIP in place.
A resistor value of 2.2K is recommended. Use other values only if you
have calculated the necessity of doing so.
5.2 TTL TO SOLID STATE RELAYS
Many applications require digital outputs to switch AC and DC voltage
motors on and off and to monitor AC and DC voltages. These AC and
high DC voltages cannot be controlled or read directly by the TTL
digital lines of a PC104-DIO48.
Solid State Relays, such as those available from Measurement
Computing Corp. allow control and monitoring of AC and high DC
voltages and can provide 750V isolation. Solid State Relays (SSRs) are
the recommended devices for interfacing to AC and high DC signals.
The most convenient way to use solid state relays with a PC104-DIO48
board is to purchase a Solid State Relay Rack. A SSR Rack is a circuit
board with output buffer chips which are powerful enough to switch the
SSR. It provides sockets for SSRs.
SSR Racks are available from the Measurement Computing Corporation.
If you only want to drive one or two SSRs, all you need is a 74LS244
output buffer chip between the 82C55 output and the SSR. Of course
the SSR will need a 5 volt power source as well.
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