Calculating Throughput; Discrete I/O Throughput Without Block Transfers; (Tdm-Nbt) Present - Allen-Bradley 1747-SN User Manual

Calculating Throughput

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
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
determine your throughput. See page A–6.
The formula to calculate the maximum scanner discrete I/O
throughput without BTs present is:
T = 2T + 2T
dm–nbt ps RIO
T = The maximum discrete throughput without BTs in
dm–nbt
milliseconds (ms)
To calculate T throughput, substitute values for the variables in
dm–nbt
the formula above. Locate these values in the following documents:
Variable Variable Description
The total processor scan time
T
ps
(ms)
T The total RIO scan time (ms)
RIO
The adapter throughput delay.
T
For a 1747 ASB, this is two
adp
ASB backplane scan times.
The scanner module output
T
SNo
delay time (ms)
The scanner module input
T
SNi
delay time (ms)
The input module delay time
T
id
(ms)
The output module delay time
T
od
(ms)
Specifications
) Present section to
dm–bt
+ T + T + T + T
adp SNo SNi id
Location of Variable
APS reference manual
see the section RIO Scan Time
Calculation (T
A-4
adapter user manual
see the section RIO Scanner
Output Delay Time (T
page A-11
5 ms (constant value for all
formulas in this appendix)
I/O product data and I/O
instruction sheets
I/O product data and I/O
instruction sheets
Publication 1747 6.6 - July 1996
A–3
)
dm-nbt
+ T
od
) on page
RIO
) on
SNo