A-D Key Identification - Sanyo C21ZM45 Training Manual

2-1 A-D Key Identification Circuit
The key identification circuit used in this chassis uses a switched resistive ladder network in a
A-D conversion circuit to generate and send a voltage to the CPU when a key is pressed.
The CPU uses this voltage to determine which key was pressed. This resistive circuit
eliminates the need for encoder/decoder devices, simplifying design and adding to the
reliability of the TV.
The table shows the voltages input to CPU pin 34 and 35, when a given key is pressed.
CPU
35
34
[${
10Ok
K1
g
100k
18k K2
~
18k
6.8k K3
~
6.8k
—
4.7k
~ &o
4.7k
2.7k
~ &l
2.7k
2.2k K6
K12
2.2k
0.27k
0.27k
10k
10k
'w
Inputvoltageto pin
34
Inputvoltageto pir _
Key
Rangeof Voltages Function
K1 0.7V- 1.5V
Pos.+
K2
1.5V-'2.lV
Pos.-
K3
2.1V -- 2.9V vol.
+(Tu
slow)
K4 2.9V- 3.5V
vol.
-(Tu
slow)
K5
3.5V--4.3V
Vol.+(TuFast)
morethan4.3V
Vol.
-(Tu Fast)
::F
less than 0.7V
No Key
-.
Kev I
Range of Voltages I Function
K7
0.7V-1 .5V
Function
K8
1.5V-2.lV
Preset1
K9
2.lV - 2.9V Preset2
K1O
2.9V- 3.5V
Colour System
K11 3.5V--4.3V
SIFSystem
K12
morethan4.3V
TV/AV
OFF
lessthan0.7V
NoKey
When the supply voltage is 5.OV.
A7-A
-7-
A7-A