ST92F124 datasheet(35/426 Pages) STMICROELECTRONICS

35 / 426 page

35/426

ST92F124/F150/F250 - DEVICE ARCHITECTURE

SYSTEM REGISTERS (Cont’d)

If the bit is set, data is accessed using the Data

Pointers (DPRs registers), otherwise it is pointed

to by the Code Pointer (CSR register); therefore,

the user initialization routine must include a Sdm

instruction. Note that code is always pointed to by

the Code Pointer (CSR).

Note: In the current ST9 devices, the DP flag is

only for compatibility with software developed for

the first generation of ST9 devices. With the single

memory addressing space, its use is now redun-

dant. It must be kept to 1 with a Sdm instruction at

the beginning of the program to ensure a normal

use of the different memory pointers.

2.3.3 Register Pointing Techniques

Two registers within the System register group,

are used as pointers to the working registers. Reg-

ister Pointer 0 (R232) may be used on its own as a

single pointer to a 16-register working space, or in

conjunction with Register Pointer 1 (R233), to

point to two separate 8-register spaces.

For the purpose of register pointing, the 16 register

groups of the register file are subdivided into 32 8-

be pointed to in twin 8-register mode, or to the low-

er 8-register block location in single 16-register

mode.

The Set Register Pointer instructions srp, srp0

and srp1 automatically inform the CPU whether

the Register File is to operate in single 16-register

mode or in twin 8-register mode. The srp instruc-

tion selects the single 16-register group mode and

specifies the location of the lower 8-register block,

while the srp0 and srp1 instructions automatical-

ly select the twin 8-register group mode and spec-

ify the locations of each 8-register block.

There is no limitation on the order or position of

these register groups, other than that they must

start on an 8-register boundary in twin 8-register

mode, or on a 16-register boundary in single 16-

The block number should always be an even

number in single 16-register mode. The 16-regis-

ter group will always start at the block whose

number is the nearest even number equal to or

lower than the block number specified in the srp

instruction. Avoid using odd block numbers, since

this can be confusing if twin mode is subsequently

selected.

Thus:

srp #3

will be interpreted as srp #2 and will al-

low using R16 ..R31 as r0 .. r15.

In single 16-register mode, the working registers

are referred to as r0 to r15. In twin 8-register

mode, registers r0 to r7 are in the block pointed

to by RP0 (by means of the srp0 instruction),

while registers r8 to r15 are in the block pointed

to by RP1 (by means of the srp1 instruction).

Caution: Group D registers can only be accessed

as working registers using the Register Pointers,

or by means of the Stack Pointers. They cannot be

addressed explicitly in the form “Rxxx”.

ST92F124 数据表(PDF) 35 Page - STMicroelectronics

ST92F124 数据表(HTML) 35 Page - STMicroelectronics

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载