Local Key Detection Method - Toshiba CN27E90 Technical Training Manual

8. LOCAL KEY DETECTION METHOD

15
S15-1
S15-2
S15-3
S15-4
S15-5
S15-6
S15-7
Fig. 3-6. Local key assignment
16
S16-1
S16-2
S16-3
S16-4
S16-5
S16-6
S16-7
Key No. Function
SA-02 POWER
SA-03 CH UP
SA-04 CH DN
SA-05 VOL UP
SA-06 VOL DN
SA-07 ANT/VIDEO, ADV
SA-08 MENU
Table 3-1. Local key assinment
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, 18) of
the microcomputer when a key is
pushed. With this method using two local key input terminals
( pins 17,18), 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 key among SA-01 to SA-08 is pressed, each of two
input terminal (pins 17, 18) developes
a voltage Vin corresponding to the key pressed. (The voltage
measurement and key identification
are carried out by an A/D converter inside the microcomputer
and the software.
Key No. Function
SA-01 DEMO START/STOP
31