ST10 FAMILY PROGRAMMING MANUAL
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2.2.1 - Definition of measurement units
The following measurement units are used to define instruction processing times:
[f
CPU
]:
CPU operating frequency (may vary from 1MHz to 80MHz).
[State]:
One state time is specified by one CPU clock period. Therefore, one State is used as the basic
time unit, because it represents the shortest period of time which has to be considered for
instruction timing evaluations.
1 [State]
= 1/
f
CPU[s]
; for
f
CPU = variable
= 50[ns]
; for
f
CPU = 20MHz
[ACT]:
ALE (Address Latch Enable) Cycle Time specifies the time required to perform one external
memory access. One ALE Cycle Time consists of either two (for demultiplexed external bus
modes) or three (for multiplexed external bus modes) state times plus a number of state times,
which is determined by the number of waitstates programmed in the MCTC (Memory Cycle
Time Control) and MTTC (Memory Tristate Time Control) bit fields of the SYSCON/BUSCONx
registers.
For demultiplexed external bus modes:
1
*
ACT
= (2 + (15 – MCTC) + (1 – MTTC))
*
States
= 100 n... 900 ns ; for
f
CPU = 20MHz
For multiplexed external bus modes:
1
*
ACT
= (3 + (15 – MCTC) + (1 – MTTC))
*
States
= 150ns ... 950ns ; for
f
CPU = 20MHz
T
tot
The total time (
T
tot) taken to process a particular part of a program can be calculated by the
sum of the single instruction processing times (
T
In) of the considered instructions plus an offset
value of 6 state times which takes into account the solitary filling of the pipeline:
Ttot
=TI1 + TI2 + ... + TIn + 6
*
States
T
In
The time (
T
In) taken to process a single instruction, consists of a minimum number (
T
Imin)
plus an additional number (
T
Iadd) of instruction state times and/or ALE Cycle Times:
TIn
=TImin + TIadd
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