Fisher MT-750 - Key Scan Operation

FUNCTIONAL DESCRIPTION Ccontinuea)
Key Scan
The microcomputer analyzes the combinations of the four The output ports are PCo ~ PC3 and the input ports PDo ~ PDs
output and input ports (4 x 4 = 16 ports in total) and detects in the chart below.
which one of the sixteen buttons (START/REJECT, REPEAT,
INTRO SCAN, etc.,) on the control panel was pressed.
Microcomputer Key Scan
=
PCOG Oo Oo
PC19 Oo Oo
Output oo
OO IN FO [oO |S Fw Jr
PC2Q Oo Oo
REPEAT
:
me
CLEAR
START/
PC3Q
oo
_REJECT
INTRO
pe | 6_SCAN
a
Input PD1@
PD26
PD36
Input Ports PDo ~ PD3 are normally kept in “H” (high) level and lf Button 1 is pressed and Output Port PCo is set in “L” tevel,
Output Ports PCo ~ PCs output the signals of “L” (low) level in Input Port PDo becomes “L” level. If Button 5 is pressed and
the cycles as illustrated. When a port is in “L” level, the other Output Port PC1 is set in “L” level, Input Port PDo becomes “L”
ports are kept in “H” level. level. Thus, the microcomputer analyzes how the input and
output ports are combined and detects which button was
pressed according to the combination.
PCo
PC1
PC2
PC3
-~13-