UPD7564 datasheet(13/56 Pages) NEC

13 / 56 page

µPD7564A, 7564A(A)

INTERNAL BLOCK FUNCTIONS

2.1

PROGRAM COUNTER (PC): 10 BITS

The program counter is a 10-bit binaryc ounter to retain program memory (ROM) address information.

Fig. 2-1 Program Counter Configuration

PC9

PC8

PC7

PC6

PC5

PC4

PC3

PC2

PC1

PC0

When one instruction is executed, usually the program counter is incremented by the number of bytes of the

instruction.

When the call instruction is executed, the PC is loaded with a nkew call address after the stack memory saves

the current contents (return address) of the PC. When the return instruction is executed, the content (return address)

of the stack memory is loaded onto the PC. When the jump instruction is executed, the immediate data identifying

the destination of the jump is loaded to all or some of bits of the PC.

When a skip occurs, the PC is incremented by 2 or 3 during the machine cycle depending on the number of bytes

in the next instruction.

When the RESET signal is input, all the bits of the PC are cleared to zero.

UPD7564 Datasheet(PDF) 13 Page - NEC