11

functioning as an I/O block address decoder. DS1 selects

the interrupt priority.

U5 is used to isolate the ICM7170 from the PC databus for

test purposes. It is only required on heavily-loaded TTL

databuses - the ICM7170 can drive most TTL and CMOS

databuses directly.

Since the IBM PC/XT (Note 1) requires a positive interrupt

transition, the ICM7170s interrupt output transistor has been

configured as a source follower. As a source follower, the

interrupt output signal will swing between 0V and 2.5V.

When trimming the oscillator, the frequency counter must be

triggered on the rising edge of the interrupt signal.

TABLE 6.

BATTERIES

CRYSTALS

Panasonic

Saronix

32kHz

NTF3238

Rayovac

Statek

32kHz

CX - 1V

Seiko

2MHz

GT - 38

NOTE:

1.IBM, IBM PC, and IBM XT are trademarks of IBM Corp.

14

15

16

9

13

12

11

10

1

2

3

4

5

7

6

8

11

12

13

14

15

16

17

18

20

19

10

9

8

7

6

5

4

3

2

1

U3

1

2

3

4

5

6

7

8

9

10

11

12

16

17

18

19

20

21

22

23

24

15

14

13

11

12

13

14

15

16

17

18

20

19

10

9

8

7

6

5

4

3

2

1

A11 AEN

S1

S2

S3

S4

A26 A5

A25 A6

A24 A7

A23 A8

A22 A9

A31 A0

A30 A1

A29 A2

A28 A3

A27 A4

B4 IRQ2

B23 IRQ5

B24 IRQ4

B25 IRQ3

TP1

POSITIVE INTERRUPT

C1

C2

C3

X1

R2

B1

SR2

C4

J1

C7

C5

C6

IOR B14

IOW B13

5V B3.B29

GND B1.B31

D7 A2

D6 A3

D5 A4

D4 A5

D3 A6

D2 A7

D1 A8

D0 A9

D1 OPTIONAL DIODE AND

RESISTOR SEE NOTE 8

R1

1K

S1

S2

S3

S4

74LS688

U2

ICM7170

U5

74LS245

U1

74LS139

+

-

DSI

INTERRUPT

SELECT

FIGURE 9. IBM PC INTERFACE FOR ICM7170Y

ICM7170