Kenwood TS-440S Serivce Manual page 20

TS-440S
CIRCUIT DESCRIPTIO N
2 . Digital displa y
FIP digit and segment signals are driven by the 6300 bu t
decimal point and red character signals are driven by a tran -
sistor . 8 V is used to increase the brightness of red charac -
ters . The 7800 sends display data serially at 1 MHz, but th e
clock signals are divided by two (500 kHz) in the 4080 an d
fed into the 6300 . Figure 16 shows how the frequency divi -
sion is accomplished . The 7800 sends data from its SO pi n
Switch uni t
+5v
(pin 28) and a clock signal from its SCK pin (pin 26) at ap-
prox . 1 ms intervals . After the 7800 has sent 8 bits of dat a
five times, the 7800 sends a negative enable pulse from port
B5 (pin 46) . When a decimal digit goes on, the 7800 set s
port C4 to L and when a red character goes on the 780 0
sets port C3 to H .
------------------- -
+g~
L
1~)
N_
O Q,
O
I()
e M N -
0 0 O 9 0 0 0 O U O O O 0
02 03 04 05 06
On 08
09 010 011 012 01 3
1 0 0 0 0 0 0 0 0 00 0
0 1 00
01 01 9
On 01
014 015
o c
20 bit Display buffer resisto r
IC3 TC40I3BP A/2
i
f'
p P D
7800G
46
O
28
5
C K
D 0
CL P R
10 8
9 13 S I
c
LH
contro l
circuit
20bit Serial shift resisto r
1 1 1- ---
fl-> J
IC I
pPD6300C
s o
s
IC 3
TC40I3BP B/ 2
D
26
SCK
3 2
CL PR
Fig . 16 Digital circuit
3 . Key scan inpu t
The key scan input block sends key scan signals (negativ e
pulses) from its 8255 (IC53) port C in the order of CO to C 7
(C6 and C7 are output only once when the POWER switc h
is turned on) . When a matrix crossing point switch is on, its
corresponding bit in the 8255 port A is L to enable the switc h
to be identified . Figure 13 shows the matrix . Key scan S 6
and S7 are provided for the extended function using diodes .
Key
scan matrix S
1 2 3
4 5 6
1 1 LSB 2 USB 3 CW 4
AM 5 F M
2 6
7 8 9 0 FS K
3 V/M MV
SCAN M .IN CLEAR EN T
4
RIT ZIT T-FSET 1MHz DOW N
K 5
A/B SPRIT A=B 25L 1 U . P
6 VOICE
. T SET ON CLOCK 1
100L 3 50L 2 100U 8
7 T .SET OFF 200L 4 25U 6 200U 9
8 TIMER SET CLOCK 2 400L 5 501 7 400U 10
Table 10 . Key scan matrix
20