Kenwood TS-440S Service Manual page 20

TS-440S
2. Digital d isplay
F IP digit a n d segment sig n a l s a re d riven by the 6 3 00 but
d e cima l point a n d red character sig n a l s a re d riven by a tran­
sistor. 8 V is used to i n c rease the b rightness of red cha rac­
te rs. The 7 8 00 se n ds dis p l ay d ata s e ri a l ly at 1 MHz, but the
c l o ck sig n a l s a re divided by two ( 500 kHz) in the 4 0 8 0 a n d
f e d into the 6 3 0 0 . Fig u re 1 6 sho w s h o w the frequ e n cy divi­
sio n is a ccomp lished. The 7 8 00 s e n d s d ata from its SO pin
r - -
I
I
I
L
_ _ _
0
28
p PD
7800G
85
46
26
3. Key scan input
The key s c a n input block s e n d s key s c a n sig n a l s (neg ative
p u l ses) from its 8 2 5 5 ( I C 5 3 ) p o rt C in the order of CO to C 7
(C 6 a n d C 7 a re output o n ly o n c e when the P OWER switch
is t u r n e d on). When a mat rix c rossing point s witch is o n, its
Key s c a n m a t r i x
1
2 6
3
4
K 5
6
7 T . S E T O F F
8
20
CIRCU IT D ESCRI PTION
1
- - - - - - - - - -
I
S w i t c h un i t
+ 5 V
I
I
I
I
I
I
I
I
I
I
_ _ _ _ _ _ _ _,
I C 3 TC 4 0 1 3BP A/2
I I
1 3
9 D CK
Q
10 8
CL PR
SCi<
I C 3
TC40 1 3 BP 8/2
4
D
2
CK Q
4 6
CL PR
1 2
1 L S B 2 U S B
7
V / M M · V
R I T
A / B
V O I C E
T . S ET O N
T I M E R S ET
(pin 2 8 ) a n d a c l ock sig n a l from its S C K pin (pin 2 6 ) at a p ­
p rox . 1 m s interv a l s. Afte r the 7 8 00 has s e n t 8 bits of d ata
five times, the 7 8 00 sends a neg ative e n able pulse from port
8 5 (pin 4 6 ) . When a decima l digit goes on, the 7 8 00 sets
p o rt C 4 to L and when a red cha racter goes o n the 7 8 00
sets p o rt C3 to H .
o .D (.> 'O Q) .... .. O'
2 0 b i t D i s p l a y
2 0 b i t Se r i a l
I C I
).J P D 6 300C
Fig . 1 6 D i g ital circuit
corresponding bit in the 8 2 5 5 port A is L to enable the switch
to be ide ntified . Fig u re 1 3 shows the matrix . Key scan S6
and S 7 a re p rovid ed for the exten d e d f u n ctio n u sing dio d e s .
s
3
3 cw 4
8 9
S C A N M . I N
Z I T T-F S E T
S P R I T A = B
1 00L
C L O C K 1
2 0 0 L
C L O C K 2 400L
Table 10 . Key scan matrix
� � = 2: ai co ,..._ l.D l() V f'l') N -
(!) (!) (!) (!) (!) (!) (!) (!) (!)
(!) (!) Cl C>
buf f e r res i s t o r
sh i f t resi stor
4 5
A M 5 F M
0 F S K
C L E A R
1 M H z
2 5L 1
3 50L 2
4 2 5U 6
7
5 5 0 1
so
6
E N T
D OW N
U . P
1 00U 8
200U 9
400U 1 0