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Epson RTC-72421 A, RTC-72421 B, RTC-72423, RTC-72423 A Page, MQ - 162, 3. Connection to 68-seriesMPU, 1. Connection to multiplexed bus type, 2. Connection to Z80 or compatible CPU

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RTC - 72421 / 72423

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

	8085/MCS48,51	RTC-72421/3	8085/MCS48,51		RTC-72421/3
	AD3	A3	AD3		A3
	AD2	A2	AD2	Latch	A2
	AD1	A1	AD1	Latch	A1
	AD1	A1	AD1		A1
	AD0	A0	AD0		A0
		D3			D3
		D2			D2
	Upper address bus	D1	Upper address bus		D1
	Decoder	D0	Decoder		D0
	IO/M	CS0	IO/M		CS0
	ALE	ALE	ALE		ALE
	RD	RD	RD		RD
	WR	WR	WR		WR

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

Z80, SMC84C00AC		RTC-72421/3
A3		A3
A2		A2
A1		A1
A0		A0
D3		D3
D2		D2
D1		D1
D0		D0
Upper address bus		CS0
	Decoder	CS0
IORQ or	Decoder
IORQ or		ALE
MEMRQ		ALE
MEMRQ
RD		RD
RD
WR		WR
WR

*Select IORQ or MEMRQ depending on whether the RTC maps I/O or memory of the CPU.

3. Connection to 68-series MPU

68 series MPU		RTC-72421/3
A3		A3
A2		A2
A1		A1
A0		A0
D3		D3
D2		D2
D1		D1
D0		D0
Upper address bus	Decoder	CS0
		ALE
R/W		RD
		RD
E		WR

Page - 18

MQ - 162 - 03

Contents

Page In pursuit of "Saving" Technology ,Epson electronic device "Saving Epson IS energy savings •The material is subject to change without notice (AC characteristics) When ALE is used When ALE is fixed at VDD Notes Timing registers Built-in •Microprocessor bus compatible ( tWW, tRD = 120 ns ) •Use of C-MOSIC enables low current consumption ( 5 ∝ A Max., at VDD = 2.0 V ) •Compatibility with Intel CPU bus •Address latch enable (ALE) pin compatible with multiplex bus CPUs RTC-72421 RTC-72423 Signal Pin No Input/ou tput D0-D3 1. Absolute maximum ratings Specification 2. Recommended operating conditions 3. Frequency characteristics and current consumption characteristics 4. Electrical characteristics ( DC characteristics ) 1. When ALE is used 2. When ALE is fixed at VDD 1. Register table 2. Notes 3. Functions of register bits (overview) 4. Setting the fixed-periodpulse output mode and fixed-periodinterrupt mode 5. Resetting the fixed-periodpulse output mode and fixed-periodinterrupt mode 1. Timing registers (1) S1 to Y10 registers (2) W register Count Day 2. CD register (control register D) (1) HOLD bit (D0) (2) BUSY bit (D1) (3) IRQ FLAG bit (D2) i. Interrupt processing (interrupt status monitor function) *STD.P pin output IRQ FLAG bit iii. Initial setting of IRQ FLAG bit (4) 30-secondADJ bit (D3) i. Operation of 30-secondsADJ bit i. Setting t0 and t1 ii. STD.P pin output control (ITRPT/STND=0) (ITRPT/STND=1) iii. Frequency of STD.P pin output in fixed-periodpulse output mode 4. CF register (control register F) i. Switching between 12-hourclock and 24-hourclock ii.Overwriting the 24/12 bit Power On To next process (A)Starting the count (B)Checking the status of the BUSY bit (C)Stopping and resetting the counter 2. Read/write of S1 to W registers 3. Write to 30-secondADJ bit 4. Using the CS1 pin (1) Functions •Protecting internal data during standby Make sure that the voltage input to the CS (2) Timing 1. Connection to multiplexed bus type 2. Connection to Z80 or compatible CPU 3. Connection to 68-seriesMPU 1.RTC-72421 2.RTC-72423 ∆ fT θ T ∆ fV Frequency[x10-6] Supply Voltage(VDD) [V] 1. Notes on handling (1) Static electricity (2) Noise (3)Voltage levels of input pins (4) Handling of unused pins Distributor AMERICA EPSON ELECTRONICS AMERICA, INC HEADQUARTER 150 River Oaks Parkway, San Jose, CA 95134, U.S.A