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8XC251SA, SB, SP, SQ USER’S MANUAL
6-12
Figure 6-7. Response Time Example #2
6.7.2.2 Computation of Worst-case Latency With Variables
Worst-case latency calculations assume that the longest 8XC251Sx instruction used in the pro-
gram must fully execute prior to a context switch. The instruction execution time is reduced by
one state with the assumption the instruction state overlaps the request state (therefore, 16-bit
DIV is 21 state times - 1 = 20 states for latency calculations). The calculations add fixed and vari-
able interrupt times (see Table 6-6) to this instruction time to predict latency. The worst-case la-
tency (both fixed and variable times included) is expressed by a pseudo-formula:
OSC
State Time
INT0#
Sample INT0#
Response Time = 4
Ten State
Instruction
Request
Push PC
A4154-02
FIXED_TIME VARIABLES LONGEST_INSTRUCTION++ MAXIMUM LATENCY PREDICTION=