ProSoft Technology PTQ-PDPMV1 - Manual (Page 288)

Reference PTQ-PDPMV1 ♦ Quantum Platform
User Manual PROFIBUS DP Master Network Interface Module for Quantum
Page 288 of 306 ProSoft Technology, Inc.
August 12, 2014
9.8 Calculating System Response Time
Processor, PTQ module, and PROFIBUS system response times are essentially
dependent on the following factors:
 T
SCAN
1 processor scan time (Loop1)
 T
BP
2
max. BP transfer time (Loop 2)
 T
PTQ
3 max. PTQ process time (Loop 3)
 T
MC
4 time of PROFIBUS message cycle time (Loop 4)
PTQ max. T
SR
(System Response Time) = T
SCAN
1 +
TBP
2 + T
PTQ
3 + T
MC
4
TSR = 7.0 ms + 45 ms + 2.84 ms + TSCAN1
where:
T
BP
2
= ~7.0 ms
T
PTQ
3 = max. ~45 ms
T
MC
4 = 2.84 ms (12PDPMV1s)
9.8.1 How to Calculate PROFIBUS Time: TMC4
First, a review of a few terms before getting into the details of calculating bus
cycle times:
Bit-Time: To help simplify timing calculations, it is convenient to normalize the
time units with respect to the baud rate by using units of Bit-Time (Tbit). One bit-
time is the time it takes to transmit one bit and is the reciprocal of the
transmission rate (baud rate). For example:
 1 Tbit (Bit Time) at 12 MB = 1/12000000 bps = 83 ns/bit
 1 Tbit (Bit Time) at 1.5 MB = 1/1500000 bps = 667 ns/bit
Sync-Time (T
SYN
)
The synchronization time is the minimum time a station must remain in the idle
state before it can accept another request. For PROFIBUS DP, an idle state of
33 Tbits (bit-time) must be present before every request telegram and this is
called the sync-time.
Slave Reaction Time (T
SDR
)
The reaction time is the time it takes a slave to respond to a message. This time
is often expressed as a minimum value (min T
SDR
), or maximum value (max
T
SDR
). Min T
SDR
is set within the parameterization telegram during startup. Max
T
SDR
varies with the transmission rate and is specified at the supported baud
rates within the device GSD file. For PROFIBUS DP, this value may range from a
minimum of 11 Tbits (min T
SDR
default) to a maximum of 255 Tbits.
Initiator Delay Time (T
SDI
)
T
SDI
refers to the station delay of the initiator of a request or token frame (the
Master).