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PIC Application Examples

Example 1 - Single PIC Application

Figure 2 shows all the connections required between CPU

and PIC to handle eight levels of interrupt control.

Programming

Programming the PIC consists of the following steps:

1. Disable interrupt at CPU

2. Reset Master Interrupt Bit, B3, of Control Register.

3. Write a “1” into the Interrupt Input bit location of the Mask

Register, if masking is desired.

4. Write the High-Order Address byte into the Page

Register.

5. Write the Low-Order Address and the vector interval into

the Control Register.

6. Program R(1) of the CPU to point to the PIC so that the

Long Branch instruction can be read from the PIC during

the Interrupt Service routine.

Values for Example 1 with LOCATION 84E0 arbitrarily cho-

sen as the Vector Address with interval of eight bytes, IR4

pending, is shown in Table 1.

In deriving the above addresses, all Don’t Care bits are

assumed to be 0.

When an INTERRUPT (IR4) is received by the CPU, it will

address the PIC and will branch to the interrupt service

routine.

The three bytes generated by the PIC will be:

FIGURE 2. PIC AND CPU CONNECTION DIAGRAM

MA7

MA6

MA5

MA4

MWR

MRD

TPA

TPB

INT

BUS

CS

CS

MWR

MRD

TPA

TPB

INT

BUS

CDP1877

CDP1802

CPU

PIC

CASC

IR7

IR6

IR5

IR4

IR3

IR2

IR1

IR0

TABLE 1. REGISTER ADDRESS VALUES

REGISTER

REGISTER ADDRESS

OPERATION

DATA BYTE

MASK

E000H

WRITE

CONTROL

E040H

WRITE

PAGE

E080H

WRITE

STATUS

E000H

READ

POLLING

E040H

READ

R(1) (IN CPU)

E080H

-

-

CDP1877, CDP1877C