Epson RTC-72421 A User Manual
RTC - 72421 / 72423
Page - 18
MQ - 162 - 03
Examples of connection to general-purpose microprocessor
When connecting the RTC-72421/RTC-72423 to a microprocessor, carefully check the AC timings of both the RTC and the
microprocessor.
1. Connection to multiplexed bus type
AD3
AD2
AD1
AD0
AD0
IO/M
ALE
RD
W R
Decoder
A3
A2
A1
A0
A0
D3
D2
D1
D0
CS0
ALE
RD
W R
8085/MCS48,51
RTC-72421/3
Upper address bus
AD3
AD2
AD1
AD0
AD0
Upper address bus
IO/M
ALE
RD
W R
Decoder
A3
A2
A1
A0
A0
D3
D2
D1
D0
CS0
ALE
RD
W R
8085/MCS48,51
RTC-72421/3
Latch
The resistors on the RD and WR lines are not necessary if the CPU does not have a HALT or HOLD state.
2. Connection to Z80 or compatible CPU
A3
A2
A1
A0
A1
A0
Upper address bus
RD
WR
Decoder
A3
A2
A1
A0
A1
A0
D3
D2
D1
D2
D1
D0
CS0
ALE
RD
WR
Z80, SMC84C00AC
RTC-72421/3
D3
D2
D1
D2
D1
D0
IORQ
MEMRQ
or
*Select IORQ or MEMRQ depending on whether the RTC maps I/O or memory of the CPU.
3. Connection to 68-series MPU
A3
A2
A1
A0
A1
A0
Upper address bus
R/W
E
Decoder
A3
A2
A1
A0
A1
A0
D3
D2
D1
D2
D1
D0
CS0
ALE
RD
WR
68 series MPU
RTC-72421/3
D3
D2
D1
D2
D1
D0