APPE~IDIX
9.9
9.9. 1
SECTIOH 9.9
SINGLE BIT INPUT PORT
The single input bit has been imple:nentcd for use with devices
such as bar-code wands, voltage free switch contacts, etc. It
is provided via the 4 pin LEHO socket pin 2. Note should be
made that it is shared with the TXCLK on the V24 interface (pin
15).
It should not, therefore, be used at the same time as the
communications when hardware handshaking is in use.
CIRCUIT IMPLEMENTATION
The input is configured as a protected, pulled up CMOS
compatible line:
Fig 9.1 CIRCUIT LAYOUT
5V
10k
100K
It has a logic 1 threshold of > 3.5V and a logic O < 1.5V. It is
protected to ±25V.
The pull-up resistor enables the use of a switch to ground to
provide the input.
No debounce circuitry is provided, If it is required then
software must be written for this purpose.
This is bit 3 on I/O port 2. See 9.8
VER. V09F PAGE 9 - 41
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