Bar Code Reader Interface Circuit - Tandy 102 Service Manual

Bar Code Reader Interface Circuit
The input signal from the bar code reader is subjected to waveform shaping, inverted by the
Schmitt-type inverter (M34), and then sent to the PC3 terminal of the PIO and the RST5.5 terminal of
the CPU.
When the bar code reader reads the first white part of the bar code, a L level signal is generated,
then inverted by M34 to notify the CPU of an interruption. As soon as RST5.5 interruption occurs,
the CPU starts the data input operation, passing through the PC3 of the PIO. As the bar code
reader is moved across the bars, H and L signals (which correspond to the white and black bars,
respectively) are generated continuously and inversion signals are sent to the PC3 of the PIO as the
serial input data stream.
BLACK LINE
WHITE LINE
VDD
BLACK LINE
WHITE LINE
CNI
Y
0
M
ti
Q:
M
I
RXD 2
13
M 12
BCR
( 8IC55-PC3)
9
VDD
Voo
RST5.5
GND
5
NC
(CPU)
GND
7
1
3
6
NC
4
8
Figure 4-10. Bar Code Reader Interface Circuit