20
Remote Control
The remote control system used is the Philip’s Enhanced RC5 protocol, with sub-address 00000.
Infra-red Transmitter
The hand unit is controlled by IC781, type PCA84C122AT/093, surface mounted on the keypad side of the
PCB. When replacing the part, the /093 is significant as it determines the key codes transmitted. Two AA
type batteries in series provide a 3V power supply.
The IC remains in standby mode (oscillator not running) until a key on the matrix is pressed. The oscillator,
governed by a 4MHz ceramic resonator XL781 is started. The IC decodes the key with suitable debounce
and then transmits the relevant code, repeating as per the RC5 specification until the key is released.
The RC5 pulse train output is modulated within the IC onto a 33.33kHz (f.osc/120) carrier with low (1:3)
hark:space ratio, reducing power consumption and allowing higher LED current. The output on pin 21 of
IC781 drives TR781 which provides high current pulses through infra-red transmitter diode D781. Reservoir
capacitor CE781 reduces momentary battery voltage drop which may otherwise affect the IC.
Infra-red Receiver
The chassis uses an integrated receiver, IC702, which provides a fully demodulated output to the
microcontroller through R703, pulled up by R702.
Keypad N°
Symbol
Functions
Keypad N° Symbol Functions
1
!
.
"
Standby 16
#
Programme Up
2 1
N°
1
17
$"
Increase Volume
3 2
N°
2
18
%"
Decrease Volume
4
3
N° 3
19
*Fastext (RED)
5
4
N° 4
20
Menu/*Fastext (GREEN)
6
5
N° 5
21
Menu/*Fastext YELLOW)
7
6
N° 6
22
Menu/*Fastext (CYAN)
8 7
N°
7
23
&"
Normalize/*Hold
9 8
N°
8
24
'"
*Expand
10 9
N°
9
25
("
*Reveal
11 0
N°
0
26
)
)
)
)"
"
Status/*Fastext Index
12
*"
TV
27
+"
AV Select
13
,"
*Text/*Mix 28
-
*Time/*Subcode
14
."
Programme Down
29
/"
**Audio Select
15
0"
Mute 30
1"
*Update
*
These functions are only present on chassis fitted with teletext
**
These functions are only present on chassis fitted with stereo
Table 3
Keypad Idents and Functions
