Datasheet
PIC16C5X
DS30453E-page 32 Preliminary 1997-2013 Microchip Technology Inc.
6.5.1 PAGING CONSIDERATIONS –
PIC16C56/CR56, PIC16C57/CR57
AND PIC16C58/CR58
If the Program Counter is pointing to the last address of
a selected memory page, when it increments it will
cause the program to continue in the next higher page.
However, the page preselect bits in the STATUS Reg-
ister will not be updated. Therefore, the next GOTO,
CALL or modify PCL instruction will send the program
to the page specified by the page preselect bits (PA0 or
PA<1:0>).
For example, a NOP at location 1FFh (page 0) incre-
ments the PC to 200h (page 1). A GOTO xxx at 200h
will return the program to address xxh on page 0
(assuming that PA<1:0> are clear).
To prevent this, the page preselect bits must be
updated under program control.
6.5.2 EFFECTS OF RESET
The Program Counter is set upon a RESET, which
means that the PC addresses the last location in the
last page (i.e., the RESET vector).
The STATUS Register page preselect bits are cleared
upon a RESET, which means that page 0 is pre-
selected.
Therefore, upon a RESET, a GOTO instruction at the
RESET vector location will automatically cause the pro-
gram to jump to page 0.
6.6 Stack
PIC16C5X devices have a 10-bit or 11-bit wide, two-
level hardware push/pop stack.
A CALL instruction will push the current value of stack
1 into stack 2 and then push the current program coun-
ter value, incremented by one, into stack level 1. If
more than two sequential CALL’s are executed, only
the most recent two return addresses are stored.
A RETLW instruction will pop the contents of stack level
1 into the program counter and then copy stack level 2
contents into level 1. If more than two sequential
RETLW’s are executed, the stack will be filled with the
address previously stored in level 2. Note that the
W Register will be loaded with the literal value specified
in the instruction. This is particularly useful for the
implementation of data look-up tables within the pro-
gram memory.
For the RETLW instruction, the PC is loaded with the
Top of Stack (TOS) contents. All of the devices covered
in this data sheet have a two-level stack. The stack has
the same bit width as the device PC, therefore, paging
is not an issue when returning from a subroutine.