PIC17C4X
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.
6.8
Bank Select Register (BSR)
The BSR is used to switch between banks in the data
memory area (Figure 6-13). In 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.
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.
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 bankinstruction is
in the instruction set.
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 6-13: BSR OPERATION (PIC17C43/R43/44)
BSR
7
4 3
0
(2)
(1)
Address
Range
0
1
2
3
4
15
SFR
Banks
10h
17h
• • •
Bank 0
0
Bank 1
1
Bank 2
2
Bank 3
Bank 4
Bank 15
15
20h
FFh
GPR
Banks
• • •
• • •
Bank 0
Bank 1
Bank 2
Bank 15
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.
2: Only Banks 0 and Bank 1 are implemented. Selection of an unimplemented bank is not recommended.
DS30412C-page 42
1996 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
