ST20-C1 datasheet(41/205 Pages) STMICROELECTRONICS

41 / 205 page

41/205

4 Using ST20-C1 instructions

4.5

Forming addresses

The addressing instructions provide access to items in data structures using short

sequences of single byte instructions. These instructions are listed in Table 4.8.

4.5.1

The address of a variable

The absolute address of a local work space location is loaded using the

ldlp primary

instruction.

ldlp 0 can be used to load the value in the Wptr.

The

ldnlp primary instruction is provided to calculate the absolute address of a non-

local variable.

The meaning of local and non-local is described in section 4.2.

4.5.2

The address of an instruction

The address of a location in the program being executed can be obtained by the

ldpi

operation as follows. The address of the location

x bytes past the next instruction

(which is itself pointed to by the instruction pointer register) can be pushed onto the

evaluation stack by

ldc x; ldpi

For example, the address of a label

L can be loaded by

ldc (L-M); ldpi

where the label

M is the address of the instruction that follows the ldpi instruction. First

the offset in bytes from

M to L is loaded into Areg. The ldpi then uses this offset and

the value in the instruction pointer register (which will be the address of label

M)to

load the address of label

L into Areg. This technique is useful for generating relocat-

able code. Breg and Creg are unaffected.

4.5.3

Arrays

The

wsub instruction interprets Areg as the address of the beginning of a vector of

word-sized data objects, and Breg as an index into that vector. After execution, Areg

holds the address of the indexed element, and Creg is popped into Breg, leaving

Areg rotated into Creg. The operation performed by

wsub is to multiply the integer in

Breg by four and to add this to the address in Areg (without overflow checking).

Mnemonic

Name

Meaning

ldlp n

load local pointer

Load the value

Wptr +4

ldnlp n

load non-local pointer

Load the value

Areg +4

ldpi n

load pointer to instruction

Load the value

Iptr + n.

wsub

word subscript

Load the value

Areg +4.Breg.

Table 4.8 Addressing instructions

ST20-C1 bảng dữ liệu(PDF) 41 Page - STMicroelectronics

ST20-C1 bảng dữ liệu(HTML) 41 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

bảng dữ liệu tải về

Link URL