9
3.2.4. printer drive circuit
Printer drive circuit consists of CPU(U17),U11,U12 and U9,U10 (driver), U13 (comparator)
Usually, P142 outputs “L” level. When one of department key is depressed, CPU outputs printer
power
Signal “H”(PR_PWR) from output port P142 of U17. Q3and Q4 turn ON. Thus the thermal head
On the printer mechanism is activated.
Serial print data input from “PR_DAT” is transferred to the shift register synchronously with the
Clock ”PR_CLK”, then stored in the latch register at the timing of the latch ”PR_/LA” signal.
The heat elements which correspond to the latched print data are activated while each gate is on.
The gates are on while each head activation signal (DST1 –DST4) is low.
3.2.5. Comparator circuit
The thermal head has a thermistor for detect the head temperature.
The level of the “TH_IN” is changed according to head temperature.
When head is heated too high temperature, the output level of comparator goes to “H” level.
Thus thermal head will be non-activity.
This status is released when the head become cool.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
J7
28FE-BT-VK-N
VP
VP
VP
VP
VP
VP
VP
VP
GND
GND
GND
GND
GND
GND
GND
GND
GND
GND
DATA OUT
CLK
LATCH
DST2
DST1
TH
VDD
DST4
DST3
DATA IN
L20
L26
L27
L28
L30
1
2
U12A
74VHC14
3
4
U12B
74VHC14
5
6
U12C
74VHC14
9
8
U12D
74VHC14
11
10
U12E
74VHC14
13
12
U12F
74VHC14
1
2
3
U11A
74VHC32
4
5
6
U11B
74VHC32
PR_PWR
PR_CLK
PR_/LA
PR_/DST1
PR_/DST2
PR_/DAT
TH_IN
PRGND
2
3
1
Q4
DTC143EUA
Q3
2SB1100
R27
10K
R28
2.2K 1/2W
R38
4.7K
R39
4.7K
R40
2.2K
R41
47K
R43
220K
R42
47K
3
2
1
8
4
U13A
LM393
L29
L31
+5V
+24V
+5V
C31
100u
50V
+5V
+5V
TH_IN
C
0
+5V
