Allen-Bradley 1747-SN - Calculating Throughput

Specifications A–3
Publication 17476.6 - July 1996
The 1747-SN Series B Scanner’s throughput is determined by using
the formulas provided in this section.
Discrete I/O Throughput without Block Transfers (T
dm-nbt
)
Present
The information in this section is used to calculate the discrete
throughput of the 1747-SN Scanner if there are no BTs occurring on
the RIO link to any chassis.
If BTs are present on the RIO link you must use the Discrete I/O
Throughput with Block Transfers (T
dm–bt
) Present section to
determine your throughput. See page A–6.
The formula to calculate the maximum scanner discrete I/O
throughput without BTs present is:
T
dm–nbt
= 2T
ps
+ 2T
RIO
+ T
adp
+ T
SNo
+ T
SNi
+ T
id
+ T
od
T
dm–nbt
= The maximum discrete throughput without BTs in
milliseconds (ms)
To calculate T
dm–nbt
throughput, substitute values for the variables in
the formula above. Locate these values in the following documents:
Variable Variable Description Location of Variable
T
ps
The total processor scan time
(ms)
APS reference manual
T
RIO
The total RIO scan time (ms)
see the section RIO Scan Time
Calculation (T
RIO
) on page
A-4
T
adp
The adapter throughput delay.
For a 1747ASB, this is two
ASB backplane scan times.
adapter user manual
T
SNo
The scanner module output
delay time (ms)
see the section RIO Scanner
Output Delay Time (T
SNo
) on
page A-11
T
SNi
The scanner module input
delay time (ms)
5 ms (constant value for all
formulas in this appendix)
T
id
The input module delay time
(ms)
I/O product data and I/O
instruction sheets
T
od
The output module delay time
(ms)
I/O product data and I/O
instruction sheets
Calculating Throughput