ST9291 ST Microelectronics, ST9291 Datasheet - Page 17

• Manufacturer Part Number: ST9291
• Description: 16-48K ROM HCMOS MCU WITH ON SCREEN DISPLAY AND VOLTAGE TUNINGOUTPUT
• Manufacturer: ST Microelectronics

SYSTEM REGISTERS (Continued)
Stack location
Care is necessary when managing stacks as there
is no limit to stack sizes apart from the bottom of
any address space in which the stack is placed.
Consequently programmers are advised to use a
stack pointer value as high as possible, particularly
when using the Register File as a stacking area.
This will also benefit programmers who may locate
the stacks in group D using, for example the in-
struction ld R237, #223 which loads the value
Figure 1-11. System and/or User Stack in
Register Stack Mode
USP R236 (ECh) System Read/Write
User Stack Pointer High Byte
Reset value: undefined
USP R237 (EDh) System Read/Write
User Stack Pointer Low Byte
Reset value: undefined
SSP R238 (EEh) System Read/Write
R255
R0
STACK POINTER L
STACK POINTER H
REGISTER FILE
STACK
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223 into the User Stack Pointer Low Register. The
Programmer will not need to remember to set the
Register Pointer to 208 to gain access to registers
in the D-group, a problem outlined in Register
Pointing Techniques paragraph.
Stacks may be located anywhere in the first 14
groups of the Register File (internal stacks) or the
data memory (external stacks). It is not necessary
to set the data memory using the instruction sdm
as external stack instructions automatically use the
data memory.
Figure 1-12. System and/or User Stack in
Memory Stack Mode
System Stack Pointer High Byte
Reset value: undefined
SSP R239 (EFh) System Read/Write
System Stack Pointer Low Byte
Reset value: undefined
1.2 MEMORY
SYSTEM REGISTERS
STACK POINTER H
STACK POINTER L
DATA MEMORY
STACK
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