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String Instructions
4-55
Assembly Language Instructions
4.8 String Instructions
Class 1, 2, 3, and 6 instructions can have string modes. During the execution
of string instruction, STR register value plus 2 is assumed as string length. An
accumulator string is a group of consecutive accumulators spanning from A
n
to the next N consecutive accumulators (N is the length of the string). The STR
register should be loaded with N–2 to define a string length, N. A value of zero
in the STR register defines a string length of 2 (string length 1 means the
instruction is not in string mode). Arithmetic string instructions treat the string
as an N word arithmetic value. The result is also an arithmetic value of the
same length. Conditionals are set as they would be set without string mode.
Comparing two strings is equivalent to comparing each bit of the string. The
accumulator status is modified representing the outcome of the entire
operation. Examine the following examples.
Table 4–43. Initial Processor State for String Instructions
Registers (
register
# =
value
)
AP0 = 2 AP1 = 21 (0x15) AP2 = 11 (0x0B) AP3 = 29 (0x1D)
AC0 = AC1 = AC2 = AC3 =
AC4 = AC5 = AC6 = AC7 =
AC8 = AC9 = AC10 = AC11 = 0xAAAA
AC12 = 0xAAAA AC13 = 0xAAAA AC14 = 0xAAAA AC15 = 0xAAAA
AC16 = AC17 = AC18 = AC19 =
AC20 = AC21 = 0x1223 AC22 = 0xFBCA AC23 = 0x233E
data memory (*
address
=
data
)
*0x0200 = 0x12AC *0x0201 = 0xEE34 *0x0202 = 0x9086 *0x0203 = 0xCDE5
program memory (*
address
=
data
)
*0x1400 = 0x0123 *0x1401 = 0x4567 *0x1402 = 0x89AB *0x1403 = 0xCDEF
*0x1404 = 0xFEDC *0x1405 = 0xBA98 *0x1404 = 0x7654 *0x1405 = 0x3210
Example 4.8.1 MOV STR, 4–2; string length = 2
MOVS A0, 0x1400
Refer to initial the processor state in Table 4–43. A0 points to AC2. Consider
a program memory location string of length 4 at 0x1400 =
0xCDEF89AB45670123. STR equal to 4–2=2, defines a string length of 4.
Final result, AC2=0x0123, AC3=0x4567, AC4=0x89AB, and AC5=0xCDEF,
Example 4.8.2 MOV STR, 3–2; string length = 3
ADDS A1~, A1, *0x0200
Refer to the initial processor state in Table 4–43. A1 is AC21, A1~ is AC5, the