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Appendix E - RTU Stand-Alone Tasks

When communications with the host are interrupted, the Remote Terminal Unit switches to Stand-Alone mode to enable it to work independently of the host. Stand-Alone controls are implemented by the Stand-Alone task (SATSK) which runs once every second to determine whether Stand-Alone control should be active:

Stand-Alone control uses pre-coded algorithms (sequences of instructions). The data that the algorithms act on are "points" such as AIs (analog inputs), DIs (digital inputs), SPs (setpoints), DVs (digital outputs), and AOs (analog outputs). Specific points are not pre-coded in the algorithm. Instead, the point types and addresses are coded in a control block.

The 25x85 Logic Processor contains both Foreground and Background (Stand-alone) controls that work alone or in combination with commands from the host. Foreground control algorithms (control blocks) run continuously, all of the time. Background control blocks run only when communications with the host have been lost or the RTU has been placed in a FORCED Stand-Alone mode.

Control blocks direct the execution of algorithms. Control blocks specify which algorithm is used, how often it is executed, and other data. A control block can refer to only one algorithm but an algorithm can use the information from any control block that refers to it. Control blocks are stored on the Remoter Terminal Unit's Solid State Disk (SSD). During RTU startup, they are copied from the SSD to RAM. The RAM copy of the control block is used at execution time.

The 25x86 8602 Control Panel contains a Stand-Alone Active switch that can be set the RTU to one of three modes of operation.

· INHIBIT: If the Stand-Alone switch on the RTU Control Panel is in the INHIBIT position, neither Foreground nor Background control blocks will be executed. SATSK reschedules itself to run again in one second.

· FORCED: If the Stand-Alone switch is in the FORCED position, both Foreground and Background controls are active - regardless of the status of communications with the host and all control blocks will run, all of the time. This provides a way to locally activate Stand-Alone controls during normal communication periods.

· AUTO: If the Stand-Alone switch is in the AUTO position and the RTU is in normal communication with the host (or NCC), control blocks designated as Foreground will run continuously and control blocks designated as Background will not run at all. Should communication with the host be interrupted for more than the length of time specified in the configuration EEPROM, Stand-Alone controls are activated until communication with the host is re-established and control blocks designated as Background will run.

RTU Control Blocks

A control block is 32 bytes in length.  It consists of a "header" (5 bytes) followed by the "body" (27 bytes). The header provides control information to the DDC program and determines the format of the control block body.

Table E-1 - Control Block Header Bytes

Byte #

Byte Description

00

Algorithm Type Code

01

Algorithm Control and Status

02

Internal Error Status

03

Delay Counter

04

Repeat Time in Seconds

Table E-2 - Time-Scheduling Bytes

Byte #

Byte Description

05

Start Time Hour

06

Start Time Minute

07

Stop Time Hour

08

Stop Time Minute

09

Day(s) of occurrence

Byte 00

Identifies the type of algorithm.

· 00 - Indicates skip this control block.

· FF - Indicates the end of the control blocks

Byte 01

Contains control and status information (indicates, for example, whether it is running in Foreground or Stand-Alone).

Byte 02

Set when an error flag bit is set in the status byte (byte 01).

Byte 03

Contains the Delay Counter value. The initial value of this counter is set to zero. After the control block runs, DDC resets the Delay Counter to the Repeat Time (byte 4) for the algorithm to run again on the next interval.

Byte 04

Specifies the Repeat Time, the period at which the control block will be run again.

Bytes 05 - 09

Used by those blocks that allow time scheduling. These bytes contain Start, Stop, Day of Week, and Holiday information.

Bytes 10 - 31

Contain parameters unique to the type of algorithm. Examples are temperature settings and point addresses.

Control Block Scheduling

The optional control block time parameters define a period of time during a particular day or days, for example, holidays from noon to 1 PM, or Monday through Friday from 8 AM to 5 PM.  Each scheduled period has a Start Time (a beginning), a Stop Time (an ending), and specified Days of the Week.

All blocks that have time scheduling capability are active or inactive depending on the day of the week. Some become active at a specified time of day, others select an operation by the time of day. See Error! Reference source not found.- Days of the Week Bit Patterns.

Table E-3 - Days of the Week Bit Patterns

Day

Bit Number

Symbol

Monday

7

MON

Tuesday

6

TUE

Wednesday

5

WED

Thursday

4

THU

Friday

3

FRI

Saturday

2

SAT

Sunday

1

SUN

Holiday

0

HOL

If, for example, you want the control block to run only on weekends and holidays, the bit pattern would be: 00000111 binary or 07 hex. The days can be specified symbolically using the symbols shown, e.g., MON+TUE+WED for Monday, Tuesday and Wednesday. On the specified days, the control block will become "active" between the designated Start and Stop Times.

NOTE: When NO time parameters are stated, or all 5 parameters are set to 0, the control block runs regardless of the time of day or day of week. A single time parameter of -1 must be specified for non-scheduled algorithms.

Algorithm Types

Each RTU normally contains only those algorithm types required or specified for the system. Algorithm types may be standard or customized to meet specific needs. Appendix F lists the common 25x85 control blocks that can be defined in byte 00, the first byte of the control block.

Control blocks are maintained through the use of the HSQ MISER CBM utility program. Refer to the HSQ MISER System Manual for program specifics. Standard control blocks are listed in Appendix F of this manual. Each control block listing shows the control block numbers, the function of each control block, and what each byte in the control block represents.

Status Byte Codes

Table E-4 lists possible values that can occur in the Control Block Status byte (byte 01). Note that if more than one status value applies, the values are added together. For example, if Foreground (08) is set, CPA has PWM output (20), and a fatal error occurs (02), the Status byte value will be 2A.

Table E-4 Control Block Status Byte (Byte 01)

Hex Value

Meaning

Comments

00

Stand-Alone Mode

 

01

Non-Fatal Error

See Tables E-4 and E-5

02

Fatal Error

See Tables E-4 and E-5

04

***

Unused

08

Primary Mode

Foreground mode

10

CPA: Raise/Lower Output

If neither CPA bits are set, then

20

CPA: PWM Output

CPA does Start/Stop output

40

OPSTR, OPSTP

Cooling mode

80

Disable Control Block

 

Error Byte Codes

Table E-5 Additional RTU Error Codes

Decimal
Value

Hex
Value


Meaning

33

21

Invalid Command

34

22

Point Invalid

35

23

Point Disabled

36

24

Invalid Memory Request

37

25

Memory Exhausted

38

26

Point Type Invalid

39

27

Point Undefined

40

28

Outputs Disabled

41

29

Invalid Configuration Code

42

2A

Unused

43

2B

Invalid MUX ID

44

2C

MUX Down

45

2D

MUX Disabled

46

2E

Max. Starts Per Hour

47

2F

Min. On/Off Time Not Met

48

30

Low Control Ownership Level

49

31

Invalid RTU ID

50

32

Invalid Access Level

Table E-6 Control Block Error Codes

Decimal
Value

Hex
Value


Meaning

1

01

Invalid Algorithm Type

2

02

Invalid Input Point

3

03

Invalid Output Point

4

04

Input Point Disabled

5

05

Output Point Disabled

6

06

Invalid CB Field

7

07

CPA: Position HI Limit

8

08

CPA: Position LO Limit

9

09

CPA: Sample Hi Limit

10

0A

CPA: Sample Lo Limit

11

0B

Units Conversion Error

12

0C

Result Out-of-Range

13

0D

4 - 20 Ma Sensor Limit Error

PID Control Block Status Codes

17

11

Setpoint at Hi Limit

18

12

Setpoint at Lo Limit

19

13

Process Variable (AI) at Hi Limit

20

14

Process Variable (AI) at Lo Limit

21

15

Output at Hi Limit

22

16

Output at Lo Limit

© 2000 HSQ Technology

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