Kenwood TS-440S Service Manual page 21

4. Static input
7800 ( IC I)
c o
Encod e r U/D sig n a l
C 2 U n l o ck sig n a l
07
40 5 2 ( IC : Dis p l ay)
8 2 5 5 ( IC 5 3)
BO Lock switch
B 2
A T switch
B 3 M IC UP switch
B 4 MIC D OWN switch
B 5 PTT s witch
B 7 V S - 1 busy sig n a l
Table 11 .
5 . A/D co nvertor in put
V o ltages contro l l e d by the RIT and IF shift VRs are a p p lied
to the 4052 ( IC 2 : Dis p l ay) . The 40 5 2 has four a n a l o g inputs :
AO ( IC 2 pin 4) is c o n n ected to the IF shift VR, a n d A 1 (pin
5) is c o n n ected to the RIT VR, the other two in puts a re not
used . When reading IF shift d ata, the 7800 sets port C5 to
0 and selects 40 5 2 AO. A s a resu lt, the 3 2 5 5 s e n ds a posi­
tive p u l s e from p o rt BO to reset the 40 5 2, a n d the 7800
sends nine positive pu lses from port C6, and port C7 receives
d ata . When reading RIT d ata, the 7800 sets CO from the
4 0 5 2 to H a n d the re after performs the same o p e rations as
when reading IF shift d ata .
I ) R I T
I K
I O K
4.7K
CIRCUIT DESCRIPTION
" H " when U P
" L " when u n l ock
A ID convertor d ata
" L " whe n switch o n
" L " whe n switch o n
" L " whe n switch o n
" L " when switch o n
" L " whe n switch o n
" H " when V S - 1 busy
2 ) I F SH I FT
+av
M O O E
4 0 5 2
::
_
_ _
A K
D O
D convert e r I n p u t
A /
Fig . 1 7 A / D convertor circuit
6 . AT control
When the AT switch is turned o n with the A UTO/THRU
switch in the A UTO position, 8 2 5 5 ( IC 5 3) ports 82 a n d 8 5
g o o n . When the 7 8 0 0 knows that the A T switch i s o n via
port 8 2, it wil l enter the CW-mod e, a n d sets p o rt A2 to H
a n d AO, A 1 , a n d A 3 to A6, a n d B4 to L , a n d transfer a pow­
e r down sig n a l . The 7800 the n knows that the PTT s witch
is o n via 8 2 5 5 p o rt 8 5, a n d sets port A6 (transmission con­
trol sig nal) to H, enabling transmission . However, if the select­
ed freq u e ncy does not a l l o w the 7 8 0 0 to p r e p a re for
tran smissio n, 7800 p o rt A6 remain s L a n d the 7800 wil l n ot
enable transmission . When the selected freq uency is 1 .9 MHz
or l ess, the 7800 wil l n ot enter CW mode n o r s e n d a power
d o w n sig n a l .
7 . LED output
D e pe n ding o n the mode, the 7800 makes the 8 2 5 5 ( IC 2)
s e n d M, SCR, 1 MHz, a n d l ock LED sig n a l s f rom p o rts B 4 ,
B 5, a n d B6. Whe n t h e LED goes on, these p o rts a re L .
W h e n the mode L E D is o n , 7800 p o rts AO to A 5 a re H . AO
to A5 correspond to LSB, USB, CW A M, F M, and FSK respec­
tively. Mode LED output is used a s mode control sig n a l s in
the IF u nit .
8 . VS - 1 ( o ptio n )
Whe n the voice switch i s t u r n e d o n , a n a d d ress correspond­
ing to the instru ction (n umerical d ata) e ntered is sent f rom
8 2 5 5 (IC 2) p o rts AO to A4 a n d a positive sta rt p u l s e sig n a l
i s sent from p o rt A 5 . The V S - 1 s e n d s busy sig n a l s (H) t o
8 2 5 5 (IC 5 3) p o rt 8 7 while the voice s witch i s o n . After the
voice switch goes off, an a d d ress corresponding to the n ext
instru ction a n d a sta rt sig n a l a re s e n t .
9. µPD 7800 reset circu it
The 7800 reset circuit is used to initia lize the 7800 whe n
the POWER s witch is t u r n e d o n. This circ uit s u p p lies a reset
pulse to the 7800 after the cl ock is s u p p lied to the 7800 sys­
tem cl ock i n p ut, X 1 (pin 3 1 ) . Since IC 3 remai n s on u ntil
PST520D (IC 3) pin 1 reaches 4 . 3 V, C 1 0 is n ot cha rged, e n a­
bling a reset sig n a l to be s u p p lied . When pin 1 exceeds 4 . 3
V , IC 3 goes off, c a u sing C 1 0 t o cha rge via R 2 a n d R 3 a n d
the reset sig n a l is removed .
T S -440S
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RIT
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