PIC17C44-08SLASHP datasheet(42/240 Pages) MICROCHIP

42 / 240 page

PIC17C4X

DS30412C-page 42

6.8

Bank Select Register (BSR)

The BSR is used to switch between banks in the data

memory

area

(Figure 6-13).

the

PIC17C42,

PIC17CR42, and PIC17C42A only the lower nibble is

implemented. While in the PIC17C43, PIC17CR43,

and PIC17C44 devices, the entire byte is implemented.

The lower nibble is used to select the peripheral regis-

ter bank. The upper nibble is used to select the general

purpose memory bank.

All the Special Function Registers (SFRs) are mapped

into the data memory space. In order to accommodate

the large number of registers, a banking scheme has

been used. A segment of the SFRs, from address 10h

to address 17h, is banked. The lower nibble of the bank

select register (BSR) selects the currently active

“peripheral bank.” Effort has been made to group the

peripheral registers of related functionality in one bank.

However, it will still be necessary to switch from bank

to bank in order to address all peripherals related to a

single task. To assist this, a MOVLB bank instruction is

in the instruction set.

For the PIC17C43, PIC17CR43, and PIC17C44

devices, the need for a large general purpose memory

space dictated a general purpose RAM banking

scheme. The upper nibble of the BSR selects the cur-

rently active general purpose RAM bank. To assist this,

a MOVLR bank instruction has been provided in the

instruction set.

If the currently selected bank is not implemented (such

as Bank 13), any read will read all '0's. Any write is com-

pleted to the bit bucket and the ALU status bits will be

set/cleared as appropriate.

Note:

Registers in Bank 15 in the Special Func-

tion

area,

are

reserved

for

Microchip use. Reading of registers in this

bank may cause random values to be read.

FIGURE 6-13: BSR OPERATION (PIC17C43/R43/44)

74 3

10h

17h

BSR

• • •

20h

FFh

• • •

(1)

(2)

Bank 15

Bank 4

Bank 3

Bank 2

Bank 1

Bank 0

Bank 2

Bank 1

Bank 0

Bank 15

SFR

Banks

GPR

Banks

Address

Range

Note 1:

Only Banks 0 through Bank 3 are implemented. Selection of an unimplemented bank is not recommended.

Bank 15 is reserved for Microchip use, reading of registers in this bank may cause random values to be read.

Only Banks 0 and Bank 1 are implemented. Selection of an unimplemented bank is not recommended.

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