PIC12C67X datasheet(70/129 Pages) MICROCHIP

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PIC12C67X

DS30561B-page 70

10.1

Special Function Registers as

Source/Destination

The PIC12C67X’s orthogonal instruction set allows

read and write of all file registers, including special

function registers. There are some special situations

the user should be aware of:

10.1.1

STATUS AS DESTINATION

If an instruction writes to STATUS, the Z, C and DC bits

may be set or cleared as a result of the instruction and

overwrite the original data bits written. For example,

executing CLRF STATUS will clear register STATUS,

and then set the Z bit leaving 0000 0100b in the reg-

ister.

10.1.2

TRIS AS DESTINATION

Bit 3 of the TRIS register always reads as a '1' since

GP3 is an input only pin. This fact can affect some read-

modify-write operations on the TRIS register.

10.1.3

PCL AS SOURCE OR DESTINATION

Read, write or read-modify-write on PCL may have the

following results:

Read PC:

PCL

→ dest

Write PCL:

PCLATH

→ PCH;

8-bit destination value

→ PCL

Read-Modify-Write:

PCL

→ ALU operand

PCLATH

→ PCH;

8-bit result

→ PCL

Where PCH = program counter high byte (not an

addressable register), PCLATH = Program counter

high holding latch, dest = destination, WREG or f.

10.1.4

BIT MANIPULATION

All bit manipulation instructions are done by first read-

ing the entire register, operating on the selected bit and

writing the result back (read-modify-write). The user

should keep this in mind when operating on special

function registers, such as ports.

PIC12C67X Datasheet(PDF) 70 Page - Microchip Technology

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