ST9291J5 datasheet(14/20 Pages) STMICROELECTRONICS

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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.

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.

SYSTEM REGISTERS (Continued)

GROUP F

VA00097

WORKING

255

240

239

r15

GROUP E

GROUP 4

224

Figure 1-9. Single 16 Register pointing Mode

GROUP F

VA00098

255

240

239

224

r15

GROUP E

GROUP 8

GROUP 3

WORKING REGISTER

Figure 1-10. Double Register pointing Mode

ST9291

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