ProSoft Technology ProTalk PTQ-PDPMV1 User Manual page 288

Reference
User Manual
9.8 Calculating System Response Time
Processor, PTQ module, and PROFIBUS system response times are essentially
dependent on the following factors:
 1
T processor scan time (Loop1)
SCAN
 2
T max. BP transfer time (Loop 2)
BP
 3
T max. PTQ process time (Loop 3)
PTQ
 4
T time of PROFIBUS message cycle time (Loop 4)
MC
PTQ max. T
SR
TSR = 7.0 ms + 45 ms + 2.84 ms + TSCAN1
where:
2
T = ~7.0 ms
BP
3
T = max. ~45 ms
PTQ
4
T = 2.84 ms (12PDPMV1s)
MC
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
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
T ). Min T
SDR SDR
T varies with the transmission rate and is specified at the supported baud
SDR
rates within the device GSD file. For PROFIBUS DP, this value may range from a
minimum of 11 Tbits (min T
Initiator Delay Time (T
T refers to the station delay of the initiator of a request or token frame (the
SDI
Master).
Page 288 of 306
(System Response Time) = T
)
)
SDR
is set within the parameterization telegram during startup. Max
default) to a maximum of 255 Tbits.
SDR
)
SDI
PROFIBUS DP Master Network Interface Module for Quantum
1 2
+ + T
SCAN TBP
), or maximum value (max
SDR
PTQ-PDPMV1 ♦ Quantum Platform
3 4
+ T
PTQ MC
ProSoft Technology, Inc.
August 12, 2014