C868_02 Datasheet, PDF (27/244 Pages) Infineon Technologies AG – 8 - Bit CMOS Microcontroller

C868
Memory Organization
Reset initializes the stack pointer to location 07_H and increments it once to start from
location 08_H which is also the first register (R0) of register bank 1. Thus, if one is going
to use more than one register bank, the SP should be initialized to a different location of
the RAM which is not used for data storage.
3.3
Program and Data Memory Organisation
The C868 can operate in four different operating modes (chipmodes) with different
program and data memory organisations:
– Normal Mode
– Normal XRAM Mode
– Bootstrap Mode
– Bootstrap XRAM Mode
3.3.1 Special function register SYSCON1
There are four control bits located in SFR SYSCON1 which control the code and data
memory organisation of the C868. Two of these bits (BSLEN and SWAP) cannot be
programmed as normal bits but with a special software unlock sequence. The special
software unlock sequence was implemented to prevent unintentional changing of these
bits and consists of consecutive followed instructions which have to set set two
dedicated enable bits.
SYSCON1
System Control Register 1
7
6
5
4
ESWC
SWC
-
-
w
w
r
r
[Reset value: 00XXX0X0_B]
3
2
1
0
-
BSLEN
-
r
rw
r
SWAP
rw
Field
SWAP
Bits
0
Typ Description
rw SWAP Code and Data Memory
SWAP = 0 : Code and data memory are in their standard
locations (default)
SWAP = 1 : Code and data memory are swapped
The modification of this bit is by software only and must be
completed by the special software unlock sequence in
order to effect the mode change. Otherwise, this bit
automatically reverts to its previous value with the third EOI
(end of instruction) after this bit is modified. This is to
prevent any incorrect status read.
User’s Manual
3-3
V 0.4, 2002-01