HMS AnyBus DataTransfer Guide

HMS FIELDBUS SYSTEMS AB
Pilefeltsgatan 93-95
S - 302 50 Halmstad
SWEDEN
Phone: +46 - 35 - 17 29 00
FAX: +46 - 35 - 17 29 09
e-mail: [email protected]
www: www.hms.se
®
DESIGN GUIDE
ANYBUS®DATATRANSFER
PARALLEL INTERFACE
Doc. No. ABDT-DGP-1.12

Design Guide
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HMS FIELDBUS SYSTEMS AB Page 2(35)
Preface.......................................................................................................................................................................4
0 Revision Notes.......................................................................................................................................................5
Index..........................................................................................................................................................................5
Date............................................................................................................................................................................5
Chapter......................................................................................................................................................................5
Author.......................................................................................................................................................................5
Revision.....................................................................................................................................................................5
1 Introduction...........................................................................................................................................................6
1.1 Terminology....................................................................................................................................................6
1.2 Background.....................................................................................................................................................6
1.3 Conditions of Trademark Use .......................................................................................................................6
2 Description of the ANYBUS DATATRANSFER Module ..................................................................................7
2.1 Interface to the Application ...........................................................................................................................7
2.1.1 Parallel Interface.......................................................................................................................................8
2.1.2 Serial Interface..........................................................................................................................................8
3 Introduction to an ANYBUS Application............................................................................................................9
3.1 Future use compatibility ..............................................................................................................................10
3.1.1 Application interface (for future use)..................................................................................................10
3.1.2 Mounting devices (for future use)........................................................................................................10
4 Dual Ported RAM Interface................................................................................................................................12
4.1 Signal Description.........................................................................................................................................12
4.2 Memory Map.................................................................................................................................................12
4.2.1 Input Area (000h - 1DFh).......................................................................................................................13
4.2.2 Output Area (1E0h - 3BFh).................................................................................................................... 13
4.2.3 Fieldbus Specific Area (3C0h - 3DFh)...................................................................................................13
4.2.4 Control Register (3E0h - 3FFh)..............................................................................................................14
4.3 Handshake Procedure..................................................................................................................................18
4.3.1 Initialisation............................................................................................................................................ 18
4.3.2 Data Exchange Mode.............................................................................................................................20
5 Interface Software Design................................................................................................................................... 23
6 Mechanical Specification.....................................................................................................................................24
6.1 Module Mechanical Drawing ...................................................................................................................... 24
6.2 Connectors..................................................................................................................................................... 25
6.2.1 Application Connector........................................................................................................................... 25
6.2.2 Fieldbus Connector................................................................................................................................25
6.3 Mounting Devices.........................................................................................................................................26
7 Electrical Specifications.......................................................................................................................................27
7.1 Application Connector Pin Description......................................................................................................27
7.2 Signal Description.........................................................................................................................................28

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7.3 Electrical Characteristics..............................................................................................................................29
7.3.1 BUS Electronics Electrical Characteristics............................................................................................ 29
7.3.2 Electronics Electrical Characteristics....................................................................................................29
7.3.3 Serial Interface Electrical Characteristics............................................................................................. 29
7.3.4 DPRAM Electrical Characteristics........................................................................................................ 29
7.3.5 RESET Electrical Characteristics........................................................................................................... 29
Appendix A Connectors........................................................................................................................................ 30
A1 Application Connectors................................................................................................................................30
A1.1 Surface Mounted........................................................................................................................................30
A1.2 Through Hole Mounted ............................................................................................................................ 30
A2 Recommended Connector Manufactures....................................................................................................... 32
A2.1 Molex.......................................................................................................................................................... 32
A2.2 Samtec.........................................................................................................................................................32
A2.3 Harwin........................................................................................................................................................32
Appendix B Hardware Design Examples ............................................................................................................33
B1 Power Supply.................................................................................................................................................33
B1.1 Dual-Galvanical Isolated Supply for BUS and Electronics..................................................................33
B1.2 Galvanically Isolated Supply for BUS Electronics: .............................................................................. 33
Appendix C Fieldbus Specific Area (3C0h - 3DFh) ............................................................................................. 35
C1 InterBus..........................................................................................................................................................35
C2 Profibus-DP................................................................................................................................................... 35
Appendix D Data Sheets DPRAM........................................................................................................................ 35

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Preface
The data and illustrations found in this design guide are not binding. We reserve the right to modify our
products in line with our policy of continuous product development. The information in this design guide
is subject to change without notice and should not be considered as a commitment by HMS Fieldbus
Systems AB.
HMS Fieldbus Systems AB assumes no responsibility for any errors that may appear in this design guide.
ANYBUS® is a registered trademark of HMS Fieldbus Systems AB.
All other registered trademarks are the property of their respective holders.

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0 Revision Notes
Index
1
2
3
4
Date
97-12-02
97-12-15
98-04-25
98-07-14
Chapter
All
Future use
Author
JoJ
ChB
LMA
KaJ
Revision
Created 0.1
Revision 1.1
Revision 1.11
Revision 1.12

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1 Introduction
This Design Guide is intended to provide details necessary to implement the ANYBUS DATATRANSFER
in a product.
The ANYBUS modules constitute HMS Fieldbus Systems AB’s adaptable system, which follows the official
standard for each fieldbus interface.
1.1 Terminology
Throughout this document the term "user" refers to the person or persons who are developing a fieldbus
product based on the ANYBUS DATATRANSFER module. The end-user of the product is referred to as the
"customer".
As in all communication systems the terms "read" and "write" can be ambiguous, because their meaning
depends on which end of the link is being referenced. The convention in this document is that "read" and
"write" are always being referenced to the master end of the link.
1.2 Background
The development and increasing use of intelligent field devices in the 1980s led to the need to replace the 4-
20 mA current loop standard with an open, vendor-independent, multi-drop, bi-directional digital
communication system, commonly known as fieldbus. There was also a growing need to integrate the
various microprocessor-based intelligent field devices so that users can take full advantage of a field
network. The fieldbus is a digital communication link between control systems and attached digital
devices. It has emerged to revolutionise the control environment and device characteristic in both process
and manufacturing industries.
Fieldbus protocols are based on ISO Reference Model for Open System Interconnection (OSI-RM), ISO 7498.
However, fieldbuses commonly use only layer 1, 2, 7 of OSI-RM, layer 3 through 6 are bypassed for real-
time purpose. There is also a new User Layer added on top of the Application Layer, where distributed
control strategy is implemented and which makes fieldbuses much more than a communication network.
There are a wide range of competing bus systems on the market, which mainly focus on part of the overall
system. These facts make it hard for both the user and the customer to choose which fieldbus they should
use. The solution is the ANYBUS concept. The ANYBUS modules make it possible for the manufacturer to
provide any fieldbus system to their products, that is supported by the ANYBUS.
1.3 Conditions of Trademark Use
Please see document: ABTM-01.

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2 Description of the ANYBUS DATATRANSFER Module
The ANYBUS modules are designed to fit into applications with different complexity levels. There are three
different types of ANYBUS modules depending on the amount of data that has to be handled. There will be
an ANYBUS for all major fieldbus system and the customer does not have to consider any fieldbus specific
information, fieldbus dependent settings or installations for the design of an application product.
•ANYBUS-32 I/O. 16 digital inputs and 16 digital outputs
•ANYBUS-64 I/O. 32 digital inputs and 32 digital outputs
•ANYBUS-DATATRANSFER. 0-480 input bytes and 0-480 output bytes
The ANYBUS-DATATRANSFER can handle large amount of data and parameters that are transferred over
a fieldbus network.
The amount of data that can be sent and received by the ANYBUS module depends on the fieldbus
network that is used.
From the user's point of view all different types of ANYBUS are interfaced in the same way. The user does
not have to consider any bus specific information or fieldbus technical settings and installations.
2.1 Interface to the Application
There are two ways to access fieldbus data in the DATATRANSFER module:
•Parallel. Through a dual ported RAM memory (DPRAM).
•Serial. Through a asynchronous interface
DPRAM
1KB
SCI
Rx
Tx
RTS
Address & Data bus
ANYBUS electronics
Application side
ANYBUS side
Alternative 1
Alternative 2
Figure 1. Application interface
Note!
Since different hardware is required for the different interfaces, only one of the above mentioned access
methods can be used in one module. Also note that there is one ANYBUS DATATRANSFER module for
each fieldbus system. The synchronous interface is only available for development of customer specific
products.

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2.1.1 Parallel Interface
The parallel interface is based on a 1kB dual ported memory (DPRAM). From the users point of view the
DATATRANSFER modules have the same function as a normal RAM memory, containing all input data
and output data transferred over the fieldbus. Applications using this interface will get the best
performance of the ANYBUS module.
To prevent data loss and that incorrect data is read from the memory due to collisions, access to the data
stored in the DPRAM is controlled in a protocol.
Only the parallel interface is described in this design guide. See chapter 4 for detailed information
2.1.2 Serial Interface
Some applications can not access the dual port RAM via address and data bus, but have a free serial link.
Therefore it is possible to operate through the serial interface. The initialisation procedure will be held in a
similar way to the Dual Port RAM solution.
The serial interface is available as an asynchronous interface, RS232 with TTL level..
The asynchronous serial interface allows the ANYBUS DATATRANSFER module to exchange data
asynchronous with external microprocessors. It has a standard non-return to zero (NRZ) format (one start,
eight data, one stop and none parity bit). Several baud rates up to 38.400 bit/s are available.
Design Guide Asynchronous serial interface document: ABDT-DGA-10
DPRAMRAM
FLASH
LED´s
Reset
circuit
MICRO
CONTROLLER
Application Interface
1kx8
Data Bus
XTAL EXTAL
Serial Interface
WD
RESET
D[0..7] A[0..18]
Address Bus
FIELDBUS
INTERFACE
Oscillator
TxD
RxD
Figure 2. AnyBus DT block schematics

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3 Introduction to an ANYBUS Application
All fieldbus systems are different in their data handling capabilities (see table 1), a default set of parameters
is defined, in order to allow full interchangeability between the different fieldbus systems and for simple
use of the DataTransfer module.
Fieldbus max. in byte max. out
byte default in/out
InterBus-S 480 480 64 / 64
Profibus-DP 200 200 64 / 64
DeviceNet 255 255 64 / 64
ModBus Plus 480 480 64 / 64
ModBus RTU 480 480 64 / 64
CANopen (Q1-98) 480 480 64 / 64
Allen Bradley RIO
FIP IO (Q1-98) 64 64 64 / 64
Remote I0 141 143 64 / 64
Table 1: Supported fieldbus systems
If the default set is active, 64 Bytes of input and 64 Bytes of output information can be handled. Since for
some applications this amount of data will not be sufficient, it is possible to change the amount of data
which can be handled by the DataTransfer module.
The maximum amount of data which can be handled by the Data Transfer module is 480 bytes of input
data and 480 bytes of output data. If this amount is still not sufficient enough for your application, please
ask HMS for a customer specific implementation. Some fieldbus systems can not support large amount of
data and can not be configured for the maximum 480 bytes of data inputs/outputs
In the following chapters it is described how an implementation when using the DataTransfer module is
performed. Finally an example is provided regarding the implementation of the DataTransfer module using
the examples and standard libraries provided by HMS.
To achieve compatibility for future AnyBus products, please read chapter 3.1 first.

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3.1 Future use compatibility
3.1.1 Application interface (for future use)
The AnyBus module is accessed through the application connector. To achieve compatibility for future
AnyBus products a 34 pin connection should be implemented.
2.00 mm
2.00 mm
34.00 mm
3.00 mm
34
1
Figure 3. Application interface connector
Pin No. Name Function
1-32 See chapter 7.1
33 A10 Not used for DT module, reserved for address line 10
34 N.C. Not connected
Table 2. Interface connector pin description
3.1.2 Mounting devices (for future use)
39.00mm
2.50mm
11.00mm
39.75mm
4.00mm
Hole A.
Hole C.
Hole B.
59.50mm
Figure 4. Mounting holes
A) Conductive hole. Used to connect P.E. on carrierboard with fieldbus electronics.

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B) Isolated hole. For use with non conductive screws. Connect to P.E. on carrierboard.
C) Conductive hole. Used for improved GND connection.

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4 Dual Ported RAM Interface
The easiest method to use the data transfer module is to integrate it into the system microprocessor bus.
This is achieved by using the DPRAM interface. Through this interface the handshaking protocol and the
access to all the relevant data is made.
4.1 Signal Description
The ANYBUS module is accessed through the application connector. This connector includes the power
supply, address and data bus and control signals for the DPRAM.
To achieve compatibility for future AnyBus products, please see chapter 3.1 before implementing.
For electrical characteristics, please see section 7 and Appendix C
4.2 Memory Map
After reset or power up of the DataTransfer module the following default memory mapping can be found.
The lowest 480 Bytes (000h - 1DFh) are dedicated to the input area and the following 480 Bytes (1E0h -
3BFh) are dedicated to the output area. The remaining 64 Bytes are divided into two 32 bytes areas. The
first area is used for fieldbus specific data and the last area is taken by different control registers.
The four different areas is mapped on the memory according the following:
Address Name Description
000h - 03Fh Input data
(64 bytes) Default no. of input bytes that can be addressed by all
supported fieldbus systems.
040h - 1DFh Free
(416 bytes) Area of free bytes that can be assigned to input data
1E0h - 21Fh Output data
(64 bytes) Default no. of output bytes that can be addressed by all
supported fieldbus systems.
220h - 3BFh Free
(416 bytes) Area of free bytes that can be assigned to output data
3C0h - 3DFh Fieldbus specific data
(32 bytes)
3E0h - 3FFh Control register
(32 bytes)
Using the input- and output- length register for I/O data (3F8h - 3Fbh) makes it possible to change the size
of the input and output area within the 480 supported bytes.

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4.2.1 Input Area (000h - 1DFh)
•write only (application ⇒AB-DT)
The number of bytes for input data is specified with the register pair 3F8h, 3F9h. By default the contents of
these registers are 00 40h for 64 bytes of input. Input is specified as: Data which is read from the
environment, and written to the fieldbus.
Changes to the size of the input area is only valid during initialisation.
4.2.2 Output Area (1E0h - 3BFh)
•read only (AB-DT⇒application)
The number of bytes for output data is specified with the register pair 3FAh, 3FBh. By default the contents
of these registers are 00 40h for 64 bytes of output. Output is specified as: Data which is written to the
environment, and read from the fieldbus.
Changes to the size of the output area is only valid during initialisation.
4.2.3 Fieldbus Specific Area (3C0h - 3DFh)
•read / write (AB-DT ⇐⇒ application)
This area makes it possible to access data and functions specific for the supported fieldbus. The area should
only be used if the application needs access to this kind of data. The contents and functions in this area
differs between the different ANYBUS modules. Not all ANYBUS modules uses this area.
The area is divided into four sub areas according the following:
Address Name Description
3C0h - 3C7h Mailbox In
(8 bytes) Mailbox area for sending data and commands to the
ANYBUS module.
3C8h - 3CFh Mailbox Out
(8 bytes) Mailbox area for receiving data and commands to the
ANYBUS module
3D0h - 3D7h Configuration
(8 bytes) Area for fieldbus and module configurations like
module address, baud rate, etc.
3D8h - 3DBh Status
(4 bytes) Area containing fieldbus and module status.
read only (AB-DT ðapplication)
3DCh - 3DFh Bi directional Status
(4 bytes) Area containing fieldbus and module status.
read / write (AB-DT ïð application)

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For more information about the usage of this area see appendix C for each ANYBUS module.
Note! The application does not have to access this area to initialise and use the ANYBUS module.
4.2.4 Control Register (3E0h - 3FFh)
•read / write (AB-DT ⇐⇒application)
Through the control registers all necessary actions are done for accessing the data in the DPRAM.
Furthermore it gives additional information of the environment, e.g. fieldbus type, fieldbus active, ...
The contents of the control register can be found in the following table. The functions are described in the
following sections.
Address Name Description
3E0h - 3F2h Reserved Not used, reserved for future use.
3F3h Watch dog Module watch dog. Incremented each ms.
3F4h Baud rate Baud rate for serial interface. Please see corresponding chapter.
3F5h ID number Module ID number.
3F6h Software version Software version identifier.
3F7h Fieldbus type Supported fieldbus system identifier.
3F8h Input length (Hi) Higher byte for input size register.
3F9h Input length (Low) Lower byte for input size register.
3FAh Output length (Hi) Higher byte for output size register.
3FBh Output length (Low) Lower byte for output size register.
3FCh Fieldbus event Flag register for indication of fieldbus events.
3FDh System status Fieldbus and module status register.
3FEh Application control Application indication register. Used by handshaking protocol.
3FFh AB-DT control ANYBUS indication register. Used by handshaking protocol.
1 Watch dog (3F3h)
•read only (AB-DT ⇒application)
Register incremented each 32 milliseconds (ms) by the ANYBUS module. This is not a precision timer and
can differ +/- 10% between different ANYBUS modules. Can be used as an indication that the ANYBUS
module is operating without any errors
2 Baud rate (3F4h)
Baud rate for serial interface. Not used by the DPRAM interface, please see corresponding chapter.
3 ID number (3F5h)
•read only (AB-DT ⇒application)
This register gives an ID-number of the board in use. The ID-number can be used to identify the revision of
the used board. It is not an unique number!
4 Software version (3F6h)

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•read only (AB-DT ⇒application)
This register contains the software version in the AB-DT module.
5 Fieldbus type (3F7h)
•read only (AB-DT ⇒application)
This register indicates the fieldbus system which the AB-DT supports.
Code Function Fieldbus system
00h PDP Profibus-DP
08h IBS InterBus-S
10h LON Lonworks
18h DEV DeviceNet
20h COP CAN open
30h FIP FIP IO
38h MBP Modbus Plus
48h RIO Remote IO
Table 3. Supported fieldbus system
The list of supported fieldbus systems is continuously updated.
6 Input length (3F8h - 3F9h)
•read / write during initialisation (application ⇐⇒ AB-DT)
•read only (AB-DT ⇒application)
The word access is done in Motorola mode. The even byte consists of the upper 8 significant bits (bit 8-15;
bit 10-15 are always 0), the odd byte consists the lower significant bits (bit 0-7).
Any value set by the application that exceeds the maximum value of the fieldbus in use will be adjusted to
maximum number of inputs or outputs by the AnyBus module.
7 Output length (3FAh - 3FBh)
•read / write during initialisation (application ⇐⇒ AB-DT)
•read only (AB-DT ⇒application)
The word access is done in Motorola mode. The even byte consists of the upper 8 significant bits (bit 8-15;
bit 10-15 are always 0), the odd byte consists the lower significant bits (bit 0-7).
Any value set by the application that exceeds the maximum value of the fieldbus in use will be adjusted to
maximum number of inputs or outputs by the AnyBus module.
3F8h HIGH BYTE
3F9h LOW BYTE
3FAh HIGH BYTE
3FBh LOW BYTE
Table 4. Motorola mode representation

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8 Fieldbus event (3FCh)
•read at any time (checking if new output data is available) (AB-DT ⇒application)
•write/clear only while access to the DPRAM is permitted (AB-DT ⇐application)
These registers indicate, if there is new output data available for the application – the flag is set to 1. If the
application is using this bit in there program, it should be cleared at any time an output update was
performed.
If this flag is not used, no action is necessary since the AnyBus module will only set this flag, but never
check the contents.
Function Contents in bits: Description
New data 0000 0000
0000 0001 No new data present New data present
9 System status (3FDh)
•read / write during initialisation (application ⇐⇒ AB-DT)
•read only (AB-DT⇒application)
•read at any time (owning DPRAM is not necessary)
The status information of the AB-DT module and of the underlying fieldbus are shown in this register.
There are only two bits that can be reconfigured during initialisation and they are the bits that indicates
output-mode.
Function Contents in bits: Description
Operation mode xxxx xx00
xxxx xx01
initialisation phase
module initialised
Output mode xxxx 00xx
xxxx 01xx
if fieldbus is stopped, all outputs are reset to 0 (default)
all outputs are FREEZED
Fieldbus status xx00 xxxx
xx01 xxxx
fieldbus stopped
fieldbus is running
DPRAM owner 01xx xxxx
10xx xxxx
DataTransfer module owns the DPRAM
Application owns the DPRAM
Table 5. System status
This register is read only! It will provide information about the status of the fieldbus. During initialisation it
will contain 00h. After the initialisation is completed, valid data is available.
If the application tries to access the DPRAM more than one second the control will be forced back to the
AnyBus module. The AnyBus module is indicating this by changing DPRAM-owner from 10 to 01. The
AnyBus module waits one millisecond before it starts to accesses the DPRAM again.

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10 Application control (3FEh)
•write only (application ⇐AB-DT)
These registers are used to perform a proper handshake between the application and the AnyBus module.
A more detailed use can be found in the next chapter.
Function Contents: Description
Req. Control 02h request to have control over DPRAM
Req. Release 01h request to release control over DPRAM
Error indication 0Fh error encountered – this message occurs only during the
initialisation, if the initialisation did not finish successfully
rest Reserved for future use
Table 6. Application control
11 AB-DT control (3FFh)
•read only (AB-DT ⇒application)
These registers are used to perform a proper handshake between application and the AnyBus module. A
more detailed use can be found in the next chapter.
Function Contents: Description
Req. OK 1111 0010 OK for application to have control over DPRAM
Release OK 0000 0001 OK for application to release control over DPRAM
Error app. 1111 1111 error encountered, control stays at application
Error AB 0000 1111 error encountered, control stays at AnyBus module
rest Reserved for future use.
Table 7. AB-DT control
By looking at the high nibble of the register, the application can easy check which side that owns access to
the DPRAM according the following:
Function Contents: Description
0000 xxxx AnyBus module has control over DPRAM
1111 xxxx application has control over DPRAM
Table 8. AB-DT control overview

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4.3 Handshake Procedure
In order to ensure that consistent data always is available, on the application side as well as on the fieldbus
side, a simple handshaking procedure is introduced. In the handshaking procedure, it is always the
application taking initiative to start handshaking and the DataTransfer module will respond to it.
Since the upper two bytes in the DPRAM are used for the handshaking, it is possible to use the interrupt
signal from the DPRAM. If you are going to use the interrupt flag, or operate in poll mode depend on your
preferences. However, there is no difference in the actual operation procedure.
The operation with the DataTransfer module can be devised into two main parts. Part one initialises the
DataTransfer module and part two is performing the actual data exchange. How these parts are
functioning, can be found in the following paragraphs.
4.3.1 Initialisation
After the application has finished its own initialisation process, the initialisation of the DataTransfer
module has to be performed. These initialisation is basically done in the following steps:
1. Write 00h to the AB-DT control register (3FFh), this will ensure a stable start up for the AnyBus
DataTransfer module.
2. Requesting access to the DPRAM.
3. Receive access to DPRAM.
4. Initialise, set input/output area (3F8h-3FBh) and output mode (in 3FDh).
5. Release access to DPRAM.
6. Check if initialisation was successful.
7. How this will look in detail is shown in the following flowchart.
If the default settings are used, it is not necessary to change any values during the initialisation. However, it
is still necessary to run through the initialisation sequence, in order to reach the data exchange state.
After the initialisation is performed successfully, the DataTransfer module is in data exchange state, and
data can be exchanged with the fieldbus.
NOTE!
The initialisation is only performed once after system reset (e.g. power up)

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APP_IND = 02
(3FEh)
APP_IND = 01
Start the
initialisation
AB_IND = 00
(3FFh)
WAIT 0.1 ms
WAIT 0.1 ms
write 00h to
register
for safe start
START
request control
over DPRAM
AB_IND
=
F2
AB_IND
=
01
request OK?
SETUP
OUTPUT MODE
(3FD) AND
IO-AREA
(3F8-3FBh)
APP_IND = 0F
WAIT 0.1 ms
INIT
COMPLETE
STATUS
BIT0 =1
AB_IND
=
00
configure the
data area in
DT module;
skip if using the
default values
request release
the DPRAM
wait 0.1 m sec.
during this time
checks thet DT-
module the
the status bit
(in 3FDh) is set
respectively
release OK?
if status=1
initialised
successful
write:
error encountered
to APP_IND
wait until DT
could have
respond
restart
initialisation
with changed
parameters
initialisation
completed
Successfully
Fieldbus
Running
Yes
No
No
Yes
Yes
No
No
YES
APP IND = 02
APP IND = 01
(3FDh)
Figure 5. Initialisation

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4.3.2 Data Exchange Mode
In the data exchange mode is the actual update of input, output, fieldbus and control area performed. In
order to ensure consistent data on both sides a simple handshaking procedure is introduced. This
handshaking procedure comes in two outlines:
•POLL mode
•INTERRUPT mode
In poll mode the data exchange is handled by polling the AB-DT control register (3FFh) during the DPRAM
access procedure.
In the interrupt driven mode the polling is substituted by waiting for the interrupt.
Both handshaking forms have in common, that all action will be started by the application. To reduce
update overhead, they can check the new data flag (3FCh) before the updating of the output field is
performed. When the last feature is used, the new data flag should be cleared during the access cycle. In
order to prevent deadlocks, a time-out function should be implemented by the application, which will
either leave the procedure or re-enter it.