ST92185B STMicroelectronics, ST92185B Datasheet - Page 30

• Manufacturer Part Number: ST92185B
• Description: 16k/24k/32k Rom Hcmos Mcu With On-screen-display
• Manufacturer: STMicroelectronics

ST92185B - DEVICE ARCHITECTURE
SYSTEM REGISTERS (Cont’d)
2.3.4 Paged Registers
Up to 64 pages, each containing 16 registers, may
be mapped to Group F. These paged registers
hold data and control information relating to the
on-chip peripherals, each peripheral always being
associated with the same pages and registers to
ensure code compatibility between ST9 devices.
The number of these registers depends on the pe-
ripherals present in the specific ST9 device. In oth-
er words, pages only exist if the relevant peripher-
al is present.
The paged registers are addressed using the nor-
mal register addressing modes, in conjunction with
the Page Pointer register, R234, which is one of
the System registers. This register selects the
page to be mapped to Group F and, once set,
does not need to be changed if two or more regis-
ters on the same page are to be addressed in suc-
cession.
Thus the instructions:
spp #5
ld R242, r4
will load the contents of working register r4 into the
third register of page 5 (R242).
Warning: During an interrupt, the PPR register is
not saved automatically in the stack. If needed, it
should be saved/restored by the user within the in-
terrupt routine.
PAGE POINTER REGISTER (PPR)
R234 - Read/Write
Register Group: E (System)
Reset value: xxxx xx00 (xxh)
Bits 7:2 = PP[5:0]: Page Pointer .
These bits contain the number (in the range 0 to
63) of the page specified in the spp instruction.
Once the page pointer has been set, there is no
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PP5
7
PP4
PP3
PP2
PP1
PP0
0
0
0
need to refresh it unless a different page is re-
quired.
Bits 1:0: Reserved. Forced by hardware to 0.
2.3.5 Mode Register
The Mode Register allows control of the following
operating parameters:
– Selection of internal or external System and User
– Management of the clock frequency,
– Enabling of Bus request and Wait signals when
MODE REGISTER (MODER)
R235 - Read/Write
Register Group: E (System)
Reset value: 1110 0000 (E0h)
Bit 7 = SSP: System Stack Pointer .
This bit selects an internal or external System
Stack area.
0: External system stack area, in memory space.
1: Internal system stack area, in the Register File
Bit 6 = USP: User Stack Pointer .
This bit selects an internal or external User Stack
area.
0: External user stack area, in memory space.
1: Internal user stack area, in the Register File (re-
Bit 5 = DIV2: Crystal Oscillator Clock Divided by 2 .
This bit controls the divide-by-2 circuit operating
on the crystal oscillator clock (CLOCK1).
0: Clock divided by 1
1: Clock divided by 2
SSP
Stack areas,
interfacing to external memory.
(reset state).
set state).
7
USP
DIV2
PRS2 PRS1 PRS0 BRQEN HIMP
0