PIC17C752-08SLASHCL datasheet(56/328 Pages) MICROCHIP

56 / 328 page

PIC17C7XX

DS30289A-page 56

7.8

Bank Select Register (BSR)

The BSR is used to switch between banks in the data

memory

area

(Figure 7-12). In

the

PIC17C7XX

devices, the entire byte is implemented. The lower nib-

ble is used to select the peripheral register 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 sin-

gle task. To assist this, a MOVLB bank instruction has

been included in the instruction set.

The need for a large general purpose memory space

dictated a general purpose RAM banking scheme. The

upper nibble of the BSR selects the currently 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

completed 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 Register area, are reserved for

Microchip use. Reading of registers in this

bank may cause random values to be read.

FIGURE 7-12: BSR OPERATION

74 3

10h

17h

BSR

• • •

20h

FFh

• • •

(1)

(2)

Bank 15

Bank 8

Bank 3

Bank 2

Bank 1

Bank 0

Bank 2

Bank 1

Bank 0

Bank 15

SFR

Banks

GPR

Banks

Address

Range

Note 1: For the SFRs only Banks 0 through 8 are implemented. Selection of an unimplemented bank is not recom-

mended. Bank 15 is reserved for Microchip use, reading of registers in this bank may cause random

values to be read.

2: For the GPRs, bank 3 is unimplemented on the PIC17C752 and the PIC17C762. Selection of an unimple-

mented bank is not recommended.

3: SFR Bank 8 is only implemented on the PIC17C76X.

Bank 3

Bank 4

Bank 7

Bank 6

Bank 5

Bank 4

(Peripheral)

(RAM)

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