PIC16CR74ESLASHP datasheet(31/172 Pages) MICROCHIP

31 / 172 page

DS21993C-page 29

PIC16CR7X

3.0

READING PROGRAM MEMORY

The ROM Program Memory is readable during normal

operation over the entire VDD range. It is indirectly

addressed through Special Function Registers (SFR).

Up to 14-bit numbers can be stored in memory for use

as calibration parameters, serial numbers, packed 7-bit

ASCII, etc. Executing a program memory location

containing data that forms an invalid instruction results

in a NOP.

There are five SFRs used to read the program and

memory. These registers are:

•PMCON1

•PMDATA

•PMDATH

•PMADR

• PMADRH

The program memory allows word reads. Program

memory access allows for checksum calculation and

reading calibration tables.

When interfacing to the program memory block, the

PMDATH:PMDATA registers form a two-byte word,

which

holds

the

14-bit

data

for

reads.

The

PMADRH:PMADR registers form a two-byte word,

which holds the 13-bit address of the ROM location

being accessed. These devices can have up to 8K

words of program ROM, with an address range from 0h

to 3FFFh. The unused upper bits in both the PMDATH

and PMADRH registers are not implemented and read

as ‘0’s.

3.1

PMADR

The address registers can address up to a maximum of

8K words of program ROM.

When selecting a program address value, the MSB of

the address is written to the PMADRH register and the

LSB is written to the PMADR register. The upper MSb’s

of PMADRH must always be clear.

3.2

PMCON1 Register

PMCON1 is the control register for memory accesses.

The control bit RD initiates read operations. This bit

cannot be cleared, only set, in software. It is cleared in

hardware at the completion of the read operation.

PMCON1: (ADDRESS 18Ch)

R-1

U-0

U-x

U-0

R/S-0

reserved

—

—RD

bit 7

bit 0

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

-n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

bit 7

Reserved: Read as ‘1’

bit 6-1

Unimplemented: Read as ‘0’

bit 0

RD: Read Control bit

= Initiates a ROM read, RD is cleared in hardware. The RD bit can only be set (not cleared) in

software.

= ROM read completed

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