PIC16C925-SSLASHCL datasheet(29/182 Pages) MICROCHIP

29 / 182 page

 2001 Microchip Technology Inc.

Preliminary

DS39544A-page 27

PIC16C925/926

3.0

READING PROGRAM MEMORY

The Program Memory is readable during normal oper-

ation 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 con-

taining 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 location being

accessed. These devices can have from 4K words to

8K words of program memory, 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 memory.

When selecting a program address value, the MSByte

of the address is written to the PMADRH register and

the LSByte is written to the PMADR register. The upper

MSbits 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 REGISTER (ADDRESS 10Ch)

R-1

U-0

U-x

U-0

R/S-0

—

bit 7

bit 0

bit 7

Reserved: Read as ‘1’

bit 6-1

Unimplemented: Read as ‘0’

bit 0

RD: Read Control bit

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

in software.

= Does not initiate a read

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR reset

’1’ = Bit is set

’0’ = Bit is cleared

x = Bit is unknown

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