21
TTP-243 Bar Code Printer
Service Manua
l
3.7 Decode Circuit
D0
3
Q0
2
D1
4
Q1
5
D2
7
Q2
6
D3
8
Q3
9
D4
13
Q4
12
D5
14
Q5
15
D6
17
Q6
16
D7
18
Q7
19
OE
1
LE
11
U3
74HC373
DO0
DO1
DO2
DO3
DO4
DO5
DO6
DO7
A16
A17
A18
A19
A20
A21
A22
A23
CLKI/0
1
I1
2
I2
3
I3
4
I4
5
I5
6
I6
7
I7
8
I8
9
GND
10
OE/I9
11
I/O0
12
I/O1
13
I/O2
14
I/O3
15
I/O4
16
I/O5
17
I/O6
18
I/O7
19
VCC
20
U8
PALCE16V8
A18
A19
A20
A21
A22
A23
1
2
3
4
5
6
7
8
9
10
RN5
10K
VCC
CLKI/0
1
I1
2
I2
3
I3
4
I4
5
I5
6
I6
7
I7
8
I8
9
GND
10
OE/I9
11
I/O0
12
I/O1
13
I/O2
14
I/O3
15
I/O4
16
I/O5
17
I/O6
18
I/O7
19
VCC
20
U10
PALCE16V8
A13
A14
A15
A16
A17
A18
A19
A20
A21
A22
A23
C69
30p
A[8..23]
VCC VCC
/UCAS
/LCAS
RTC
DS
AS
ST1
ST0
/CAS
/E
/RESET
MA0
DO[0..7]
ALE
ROM2
CENTRONIC
ROM11
ROM12
Fig. 3.7 Decode Circuit
This is the decode circuit which calculates memory map. U3 is used to latch addresses
from DO0 to DO7. The main function of U8 and U10 are to decode the address and
memory control
signal .The memory map of TTP-243 is as shown in Figure 1.2.
The pin function description is as follows:
AS: The address strobe control signal of RTC.
DS: The data strobe control signal of RTC.
/CAS: The DRAM column address control pin of MCU.
/LCAS: The bank 0 column address control pin of DRAM.
/UCAS: The bank 1 column address control pin of DRAM.
RTC: The chip select pin of RTC.
CENTRONIC: Enable MCU to read data from parallel port.
ROM11: The chip select pin of U16 when system is in normal mode.
ROM12: The chip select pin of U16 when system is in BIOS update mode.
ROM2: The chip select pin of U25.
ST0: Status signal output pin of MCU.
ST1: Status signal output pin of MCU.
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