ST9291 ST Microelectronics, ST9291 Datasheet - Page 14

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

ST9291
SYSTEM REGISTERS (Continued)
EXAMPLES
Using the Single 16 Register Group
When the system is operating in the single 16-reg-
ister group mode, the registers are referred to as
r0-r15. In this mode, the offset value (i.e. the num-
ber of the working register referred to) is supplied
in the address (preceded by a small r, e.g. r5) and
is added to the Register Pointer 0 value to give the
absolute address.
For example, if the Register Pointer contains the
value 70h, then working register r7 would have the
absolute address, R77h.
In this mode, the single 16-registers group will al-
ways start from the lowest even number equal or
lower to the number given in the instruction.
Example: srp #3 is equivalent to srp #2.
Figure 1-9. Single 16 Register pointing Mode
14/20
GROUP E
GROUP 4
GROUP F
REGISTER POINTER 0
REGISTER
WORKING
r0
0
r15
VA00097
239
224
255
240
Using the Twin 8-Register Group
When working in the twin working group mode, the
registers pointed by Register Pointer 0 (RP0R), are
referred as r0-r7 and those pointed by Register
Pointer 1 (RP1R), are referred to as r8-r15, regard-
less of their absolute addresses. In this mode,
when operating with the first 8 working registers
(i.e. r0 - r7) the working register number acts as an
offset which is added to the value in Register
Pointer 0.
So if Register Pointer 0 contains the value 96, then
working register 0 has the absolute address 96,
working register 5 has the absolute address 101,
and so on. The second group of working registers,
r8-r15, has the offset values 0 to 7 respectively (i.e.
r8 has the offset value 0, r9 has the offset value 1,
and so on), this offset value being added to the
value in Register Pointer 1.
For example, given that the value in Register
Pointer 1 is 32, then working register 12 supplies
an offset value of 4 (given by 12 minus 8) to the
value in Register Pointer 1 to give an absolute ad-
dress of 36.
Figure 1-10. Double Register pointing Mode
GROUP F
GROUP E
GROUP 8
GROUP 3
REGISTER POINTER 1
REGISTER POINTER 0
WORKING REGISTER
WORKING REGISTER
0
r7
r0
r15
r8
239
255
240
224
VA00098