Date Code 20010518 SELOGIC Control Equations 7-9
SEL-2020 Instruction Manual
Processing Sequence
You may need to consider the order in which SEL
OGIC Control Equations are processed to fully
understand their operation and thereby ensure the desired result. When a SEL
OGIC Control
Equation contains, as one of its terms, the result of another SEL
OGIC Control Equation, the order
in which the equations are processed may affect the result. For example, consider three SEL
OGIC
Control Equations, A, B, and C, that are processed in alphabetic order. It takes 1 µs to process
each equation, and the group is processed every 15 ms. If SEL
OGIC Control Equation B contains
the results of equation A, the results of B will be current (within 1 µs) because A was processed
as part of the current process cycle. However, if equation B contains the results of equation C,
the results of B will not be current because the results of C are from the previous process cycle,
which is now 15 ms old.
The SEL-2020 processes SEL
OGIC Control Equation in the following order and frequency (see
Figure 7.8 for an illustration of this processing sequence):
Symbol Period Description Order
0 3.9 ms Output SEL
OGIC Control Equations OUT1 to OUT4
I 15.6 ms Intermediate Logic V,W,X,XT,Y,YT,Z,ZT
1-16 15.6 ms Port Logic (e.g. 3 = Port 3 Logic) SBR1, SBR2, …, SBR16,
CBR1, CBR2, …, CBR16
SRB1, SRB2, …, SRB16,
CRB1, CRB2, …, CRB16,
ISSUE1 to ISSUE12,
ISSUE1A to ISSUE3A,
BR1, BR2, …, BR16,
RB1, RB2, …, RB16
0,I,1,5,9,13 0,2,6,10,14 0,3,7,11,15 0,4,8,12,16
Figure 7.8: Processing Sequence Illustration
To illustrate the effects of the processing sequence, consider the following equations:
W=V Equation 1
V=W Equation 2
ISSUE1=1:UMB*!D1 Equation 3
In Equation 1, V is processed before W, so W will always exactly match V in value. However,
in Equation 2, V will always lag W by 15.6 milliseconds because V is processed before W; V is
being assigned the value W was set to during the last processing interval. In Equation 3, the
issue condition will be true for one processing interval, because D1 is found based on the
ISSUE1 value; so the D1 used in the equation will be the result of the previous processing
interval's computations.
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