8
022
UNIGYR®
VISONIK®
Process Bus
The process bus serves to exchange process-related data between the PRU and
RWP80 process units for UNIGYR or PRV units for VISONIK and the PTM I/O
modules. The process bus has been designed as a control panel bus and is thus
referred to as Panel Bus or, in short, P-bus.
Use
The P-bus is a Landis & Staefa bus to transfer process-related data. The total length for
the standard P-bus is 50 meters and 200 meters for the remote P-bus. Line connections
to neighbouring control panels are permitted.
P-bus structure
The P-bus consists of the following three lines:
P-bus
L
T1
8022Z01E
– PD data line to transfer telegrams
– PU reference voltage for PD and PC as well as DC voltage for I/O modules
– PC clock line for telegram synchronisation
G
G0
G
G0
N
N1
U1
P-bus
U2
p
p
N1
T1
U1
U2
Note
Refer to the following documentation for information on units connected to the P-bus:
–
–
–
–
–
–
–
Siemens Building Technologies
Landis & Staefa Division
PRU, PRV, RWP80 process unit
AC 230 V / AC 24 V transformer
I/O module group with outputs to the control panel units
I/O module group with outputs to external field devices
I/O Modules PTM_. ...
Data sheets 8100, 8110 to 8199, 8663 to 8666
Accessories for I/O Module System
Data sheet 8105
Universal Process Unit
PRU10.64 Data sheet 8211
Standard Process Unit
RWP80 ... Data sheet 8221
Universal Process Unit
PRU1 ...
Data sheet 8241
Controller
PRV1 ...
Data sheet 8341
Process Units
PR_2 ...
Data sheet 8411
CM2N8022E / 02.1999
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Mode of operation
The sections below explain the mode of operation for data transmission on the P-bus.
For UNIGYR and VISONIK, the terms ‘Master’ and ‘Slave’ can be replaced with
‘Process unit’ and ‘I/O module’ respectively.
Master-Slave principle
The master sends the start condition on the PC line (clock line for telegram
synchronisation) to all slaves. A slave address and the function byte is then transmitted
on the PD line (data line). The function byte determines if data is subsequently read or
written.
The master retrieves the data in the read telegram from the addressed status,
measured value, or counter module. In the case of the write telegram, the commands to
be executed are sent to the addressed switching or positioning module.
Telegram format
For read or write access, a telegram always consists of five bytes (= 40 bits). These
bytes are transmitted in the following sequence:
1.
2.
3.
4.
5.
byte
byte
byte
byte
byte
I/O module address
function, i.e., read or write access
data 1 Data contents and structure are
data 2 dependent on the I/O module function
telegram check CRC test (= Cyclical Redundancy Check)
Direction of data for the function in a polling cycle
Read:
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
Address
Function
Data 1
Data 2
CRC
Write:
7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0
Function
Data 1
Data 2
Telegram with 5 bytes = 40 bits
CRC
8022D01E
Address
Direction of data: Master-slave
Direction of data: Slave-master
Telegram termination
with telegram check
After the 40th bit, the telegram is terminated. If the transmission was error-free, an
acknowledge is sent and a not acknowledge in the case of a faulty transmission. If the
latter applies, the telegram is re-transmitted.
Note
At the given transmission rate of 62.5 kBaud (62,500 bps) over 1,000 telegrams can be
transmitted per second.
Digital signals on the
PD and PC lines
Digital signals are transmitted on the P-bus PD and PC lines. The data on PD are binary
raw values in the range of 0 to 256. They do not reflect units: conversion into physical
units (e.g., temperature measured value in °C) occurs in the process unit.
PU reference voltage
The reference voltage of ca. DC +23.5 V on the PU line is generated in the process unit.
The system neutral (=G0) represents the zero potential for this voltage.
AC 24 V operating voltage
The AC 24 V operating voltage is derived directly from the control panel transformer.
G then represents the potential line for the operating voltage (=system potential) and G0
the zero line for the operating voltage (=system neutral).
CM2N8022E / 02.1999
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Siemens Building Technologies
Landis & Staefa Division
I/O strip with module
supply block
The illustration below contains the P-bus lines and the AC 24 V operating voltage line as
arranged on the I/O strip.
L
230V~
N
24V~
T1
G
G0
G
G0
P-bus
8022V03E
PD
PU
PC
X1
G G0 PC PU PD
N1
G
G0
PD
PU
PC
G0
G
Data line
Reference voltage
Clock line
System neutral
System potential
From
master
From
transformer
PC PU PD
U1
N1
T1
U1
X1
Characteristics
PRU, PRV, RWP80 process unit (rear)
AC 230 V / AC 24 V transformer
PTX1.01 module supply block
PTX1. ... I/O strip
The P-bus has the following characteristics:
– synchronous, byte-oriented serial data transmission with telegram synchronisation by
master clock (master-slave principle)
– half duplex mode, i.e., data are only received in one direction at a time; sending or
receiving
– polling cycle 0.5 seconds, i.e., every 0.5 seconds, data transmission occurs cyclically
between the master (process unit) and each slave (I/O module), regardless of the
number of connected slaves.
Engineering notes
During engineering, the permissible total line lengths for the bus lines (50 m or 200 m)
must be observed. The total line length must include the sum of all line sections.
P-bus cable length
If the P-bus is a 3-core round cable (unshielded), the maximum total length is 50 meters
(standard P-bus). By using two shielded cables (coaxial cables), the P-bus line length
can be extended to 200 meters (remote P-bus).
Combination of standard
and remote P-bus
The P-bus can be divided into a standard P-bus section (with round cable, e.g., to
connect the process unit to the I/O modules within the same control panel) and a remote
P-bus section (with coaxial cable, e.g., for remote "I/O module islands").
In the case of a combination P-bus, the length of the remote bus section depends on the
length of the standard bus section as well as the number of connected I/O modules,
whereby one PTK1... I/O compact unit corresponds to eight I/O modules. Both P-bus
sections can be subdivided into several P-bus sections or I/O module islands.
The diagram below contains the permissible P-bus line lengths in the case of a
combination P-bus (standard and remote).
Siemens Building Technologies
Landis & Staefa Division
CM2N8022E / 02.1999
3/8
m
P-bus cable lengths
Remote P-bus
(coaxial cable)
200
190
40
I/O
m
m
od
o
ule dul
es
s*
*)
)
I/O
I/O
30
50
≤
150
*)
es
ul
od
m
100
50
m
0
0
10 12
20
30
Example: With a standard P-bus length of 12 m and a total
of 25 connected I/O modules, the maximum
permissible length of the remote P-bus is 190 m.
∧
*) 1 I/O compact unit PTK1.. = 8 I/O modules
40
50
Standard P-bus
(round cable)
8022D02E
Note
The total line lengths of 50 and 200 meters represent absolute limits. Extending the Pbus line length by adding repeaters is not possible.
Process unit with two
P-bus connections
For the PRV1.128 and PRV2.128 process units with two P-bus connections, the total
length per P-bus is relevant, i.e., a remote bus of up to 200 meters may be connected to
each P-bus connection. Consequently, connecting the standard P-bus with max. 50
meters to the first connection and the remote P-bus with max. 200 meters to the second
connection, or a combination of standard and remote P-bus connections as illustrated
above is possible.
Bus topology
Line, star, or tree-like bus topologies are permitted whereby the length of all sections
must amount to a maximum of 50 or 200 meters respectively. A ring-type P-bus
structure is not permitted.
Installation notes
Standard P-bus wiring
With the standard P-bus, the PD, PU, and PC lines are laid in a 3-core unshielded
round cable. Unshielded round cables are permitted within and outside of the control
panel.
– Ribbon cables with PU reference line in the centre are permitted; however, they are
not as immune to noise as round cables. Single wires are not permitted.
Remote P-bus wiring
CM2N8022E / 02.1999
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The remote P-bus is wired with two coaxial cables. The clock (PC) and data (PD) lines
must be connected to the inner conductor of each coaxial cable. The reference voltage
(PU) must be laid in the shielding of both coaxial cables whereby the shielding of the
two cables must be interconnected (see bottom right drawing in the wiring diagram
below). In this case, the cable shielding is used as a conductor and must not be
connected to the ground.
Siemens Building Technologies
Landis & Staefa Division
Remote P-bus Wiring diagram
Control panel
AC 230 V
G
AC 24 V
AC 24 V
I/O modules (AC 24 V)
B
AC 230 V
G0
G G
GO
G
T1
G GO
PTX1.01
PC / PU / PD
Remote P-bus
I/O modules (AC 24 V)
PC / PU / PD G GO
G0
Standard P-bus
G
C
GO GO GO
T2
PTX1.01
PC / PU / PD
A
PC
PU
PD
(P-bus)
PRU...
PRV...
G GO PC / PU / PD
PTX1.01
8022V04E
I/O modules
D
PC / PU / PD G GO
PTX1.01
PC / PU / PD
G
I/O modules (AC 24 V)
PC / PU / PD G GO
E
G0
T3
PC PD
PTX1.01
PC / PU / PD
PU
I/O modules
F
Supply of the I/O strips
or I/O module islands
PC / PU / PD G GO
RG-62A/U
G0
1.5 mm²
PTX1.01
The above wiring diagram shows a remote P-bus combined with section A as the
standard P-bus. The following must be observed for the I/O strip or I/O module island
supply:
• For I/O strips containing I/O modules, supplied with AC 24 V operating voltage
(normal), a supply transformer must be installed locally at the PTX1.01 module supply
block (I/O strips B, C, and E).
• For I/O strips containing just I/O modules requiring no AC 24 V operating voltage, a
supply transformer is not necessary (I/O strips D and F).
The following I/O modules do not require AC 24 V (G/G0) operating voltage:
– PTM1.2D20
– PTM1.2R1K, PTM1.4R1K
– PTM1.2QD, PTM1.4QD
System neutral, G0 line
Siemens Building Technologies
Landis & Staefa Division
PTM1.2D42
PTM1.2P100
PTM1.2Q250
PTM1.2D250
PTM1.2P1K
Use a single-core copper cable, 1.5 mm2 diameter, for the system neutral (G0 line). For
reasons of electromagnetic compatibility, the P-bus lines and the G0 line must be laid
parallel and a cable tie must be used every 3 to 4 meters (see bottom right drawing in
the above illustration).
CM2N8022E / 02.1999
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General installation
notes
Refer to the Mounting and Installation Handbook M8012 for PRU or M8017 for PRV for
information on installing the units to be connected to the P-bus as well as for general
wiring and earthing information.
P-bus cable connection
and operating voltage
The P-bus cable is connected to the rear side of the unit and to the PTX1.01 supply
module block. The AC 24 V operating voltage is also wired from the transformer to the
rear side of the unit and the PTX1.01 supply module block. (The AC 24 V operating
voltage and the P-bus are not directly led to the I/O modules).
System neutral, G0 line
The G0 line is wired together with the G line (AC 24 V operating voltage) in a star-like
manner from the transformer. G0 from the process unit and supply module block of the
associated I/O strip(s) must always be galvanically separated.
Network lines
For the standard as well as the remote P-bus, the P-bus cable may be laid together with
the AC 24 V operating voltage lines and the AC 3 x 400 V 3-phase network lines.
Commissioning
notes
The P-bus works properly only if PD, PU, PC, and G0 are wired. We recommend to also
wire line G of the AC 24 V operating voltage to the I/O module groups.
– If several process units are installed, ensure that the P-bus of a process unit is wired
only to the respective I/O strip(s).
– Two or several process units cannot be connected via the same P-bus.
Technical data
Standard P-bus:
Round cable for PD, PU, PC
Bus length incl. all sections
Wire diameter (for 50 m bus length)
3-core, unshielded
max. 50 m
1.5 mm2
Remote P-bus:
Two coaxial cables
Bus length incl. all sections
Characteristic impedance
Capacity
single-core (e.g., type RG-62 A/U)
max. 200 m
50 .. 120 Ohm
< 43 pF/m
Rate of transmission
Polling cycle
Bus topologies
62.5 kBaud (62,500 bps, fixed)
0.5 seconds
line, star, tree-like
We reserve the right to make changes to technical data.
Connection diagram
P-bus
24V~
PTM...
PRU... / PRV... / RWP80...
G G0
PC PU PD
G
G0
PC PU PD
PD PU PC
PTX1.01
8022V02E
P-bus
24V~
AC 24 V operating voltage
G
System potential
G0
System neutral
CM2N8022E / 02.1999
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Process bus (P-bus)
PD Data line
PU Reference voltage
PC Synchronisation line (clock)
Siemens Building Technologies
Landis & Staefa Division
P-bus characteristics
Line signals P-bus
Ulref
*
PU
Master
Rline
Udatam
Udatas
PD
Process
unit /
Controller
Umckm
Slave
R-Line
DATA
PC
I/O-modules
Ubez MCK
G0
* Protection diode in module supply block
Electrical characteristics of P-bus
Characteristic
Symbol
Reference voltage
Line
voltage drop
Min.
Typical
Max.
Unit
Uref
22
23.5
26
V
Ulref
0
0.5
V
Data transmission from master
Signal level LOW
UdatamL
UmckmL
6.6
8.0
V
Signal level HIGH
UdatamH
UmckmH
0
0.4
V
Data transmission from slave
Signal level LOW
UdatasL
5.2
8.0
V
Signal level HIGH
UdatasH
0
0.1
V
50
m
Line length
Capacitance
between lines
data
mck
m
s
U
L
H
Note
100
pF/m
8022T01E
Line characteristics
Data line
Clock line (synchronization)
Master
Slave
Signal
Low level = log 1
High level = log 0
The signal level Udata on the PD and Umck line on the PC clock line correspond to
negative logic, i.e., signal level at logical "0" is higher than at logical "1". The following
typical signal levels apply:
– at logical "0", Udata = Uref - Signal level HIGH
– at logical "1", Udata = Uref - Signal level LOW
= ca. DC +23.5 V
= ca. DC +16.5 V
Uref = Reference voltage on PU line
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Landis & Staefa Division
CM2N8022E / 02.1999
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Transition from the end of one P-bus telegram
to the start of the next
MCK
End of telegram
Start of telegram
t
t
t
1
2
3
t
4
UH
UL
40*
1*
2*
t
* = Number of positive clock edge within a telegram
Dynamic characteristics of P-bus
Min.
Last positive pulse
of a telegram
(time out)
t
Min.pause
between two
telegrams
(idle time)
t
Clock pulse HIGH
within a telegram
t
Clock pulse LOW
within a telegram
t
Rate of
transmission
1
2
3
4
Type
*)
*)
25
Max.
Unit
110
µs
µs
8
µs
8
µs
62.5
62,500
kbaud
bps
8022T02E
Characteristic
*) Times t1 and t2 characterize the quality of the telegram (acknowledge = TRUE or FALSE)
 1999 Siemens Building Technologies Ltd.
CM2N8022E / 02.1999
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Siemens Building Technologies
Landis & Staefa Division