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8. LOCAL KEY DETECTION METHOD
Local key detection in the N5SS chassis is carried out by
using analog like method which detects a voltage appears at
local key input terminals (pins 17 and 18) of the microcom-
puter when a key is pushed. With this method using two
local key input terminals (pins 17 and 18), key detection up
to maximum 14 keys will be carried out.
The circuit diagram shown left is the local key circuit. As
can be seen from the diagram, when one of keys among SA-
01 to SA-08 is pressed, each of two input terminals (pins 17
and 18) developes a voltage V
IN
corresponding to the key
pressed. (The voltage measurement and key identification
are carried out by an A/D converter inside the microproces-
sor and the software.
17
18
SA08
SA06
SA05
SA07
SA01
SA02
SA03
SA04
Fig. 3-6 Local key assignment
Table 3-1 Local key assignment
Key No. Function Key No. Function
SA-02 POWER SA-01
DEMO START/STOP
SA-03 CH UP
SA-04 CH DN
SA-05 VOL UP
SA-06 VOL DN
SA-07 ANT/VIDEO, ADV
SA-08 MENU