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23.9.7

Timer and Counter Functions Down Counter

The Down Counter function counts down from a preset value. The minimum preset value
is zero; the maximum present value is +32,767 counts. The minimum current value is

–

32,768. When reset, the current value of the counter is set to the preset value PV. When
the enable input transitions from OFF to ON, the current value is decremented by one. The
output is ON whenever the current value is less than or equal to zero.

The current value of the Down Counter is retentive on power failure; no automatic
initialization occurs at power-up.

Figure 344

Parameters of the Down Counter Function

Input/
Output

Choices

Description

address

The function uses three consecutive words (registers) of %R memory
to store the following:

•

Current value (CV) = word 1.

•

Preset value (PV)

= word 2.

•

Control word

= word 3.

Do not use this address with another down counter, up counter, or
any other instruction or improper operation will result.
Careful: Overlapping references will result in erratic counter
operation.

enable

flow

On a positive transition of enable, the current value is decremented
by one.

flow

When R receives power flow, it resets the current value to the preset
value.

I, Q, M, T, G, R,
AI, AQ,
constant, none

PV is the value to copy into the counter’s preset value when the

counter is enabled or reset.

flow, none

Output Q is energized when the current value is less than or equal to
zero.

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Example 1

In the example, the down counter identified as COUNTP counts 500 new parts before
energizing output %Q0005.

Figure 345

Example 2

The  following  example  shows  how  the  PLC  can  keep  track  of  the  number  of  parts  in  a
temporary  storage  area.  It  uses  an  up/down  counter  pair  with  a  shared  register  for  the
accumulated or current value. When parts enter the storage area, the up counter increases
the current value of the parts in storage by 1. When a part leaves the storage area, the down
counter decrements by 1, decreasing the inventory storage value by 1.  The two counters
use different register addresses. When a register counts, its current value must be moved
to the current value register of the other counter.

Figure 346

See the pages on Math functions for an example of using the Addition and Subtraction
functions to provide storage tracking.

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Chapter 24:

Service Request Function

This chapter explains the Service Request (SVCREQ) function, which requests a special PLC
service. It describes SVCREQ parameters for the VersaMax Nano PLC and Micro PLC.

•

SVCREQ Function Numbers

•

Format of the SVCREQ Function

•

SVCREQ 1: Change/Read Constant Sweep Timer

•

SVCREQ 2: Read Window Times

•

SVCREQ 3: Change Programmer Communications Window Mode

•

SVCREQ 4: Change System Communications Window Mode

•

SVCREQ 6: Change/Read Number of Words to Checksum

•

SVCREQ 7: Read or Change the Time-of-Day Clock

•

SVCREQ 8: Reset Watchdog Timer

•

SVCREQ 9: Read Sweep Time from Beginning of Sweep

•

SVCREQ 10: Read Folder Name

•

SVCREQ 11: Read PLC ID

•

SVCREQ 13: Shut Down (Stop) PLC

•

SVCREQ 14: Clear Fault

•

SVCREQ 15: Read Last-Logged Fault Table Entry

•

SVCREQ 16: Read Elapsed Time Clock

•

SVCREQ 18: Read I/O Override Status

•

SVCREQ 23: Read Master Checksum

•

SVCREQ 26/30: Interrogate I/O

•

SVCREQ 34: Enter Analog Calibration Mode

•

SVCREQ 35: Execute Analog Calibration

•

SVCREQ 52: Read from Flash

•

SVCREQ 53: Write to Flash

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24.1

SVCREQ Functions

Each Service Request has its own function number, as listed in the following table.

Function #

Description

Change/Read Constant Sweep Timer

Read Window Times

Change Programmer Communications Window Mode and Time

Change System Communications Window Mode and Time

reserved

Change/Read Number of Words to Checksum

Change/Read Time-of-Day Clock

Reset Watchdog Timer

Read Sweep Time from Beginning of Sweep

Read Folder Name

Read PLC ID

reserved

Shut Down the PLC

Clear Fault Tables

Read Last-Logged Fault Table Entry

Read Elapsed Time Clock

reserved

Read I/O Override Status

19-22

reserved

Read Master Checksum

26, 30

Interrogate I/O

27, 28

reserved

Read Elapsed Power Down Time

31-33

reserved

Enter Analog Calibration mode

Execute Analog Calibration

36-51

reserved

Read from Flash

Write to Flash

53-255

reserved

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24.2

Format of the SVCREQ Function

The SVCREQ function has three inputs and one output.

Figure 347

When the SVCREQ receives power flow, the PLC is requested to perform the function
number (FNC) indicated. Parameters for the function are located beginning at the reference
given for PARM.

This is the beginning of the “parameter block" for the function. The number

of 16-bit references required depends on the SVCREQ function being used.

Parameter blocks may be used as both inputs for the function and the location where data
may be output after the function executes. Therefore, data returned by the function is
accessed at the same location specified for PARM.

The  SVCREQ  function  passes  power  flow  unless  an  incorrect  function  number,  incorrect
parameters,  or  out-of-range  references  are  specified.    Specific  SVCREQ  functions  have
additional causes for failure.

24.2.1

Parameters of the SVCREQ Function

Input/
Output

Choices

Description

enable

flow

When enable is energized, the service request is performed.

FNC

I, Q M, T, G, R, AI, AQ,
constant

Contains the constant or reference for the requested service.

PARM

I, Q M, T, G, R, AI, AQ

Contains the beginning reference for the parameter block for
the requested service.

flow, none

OK is energized when the function is performed without error.

Example of the SVCREQ Function

In the example, when the enabling input %I0001 is ON, SVCREQ function number 7 is called,
with the parameter block located starting at %R0001. Output coil %Q0001 is set ON if the
operation succeeds.

Figure 348

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24.3

SVCREQ 1: Change/Read Constant Sweep
Timer

Use SVCREQ 1 to enable or disable Constant Sweep Time mode, change the length of the
Constant Sweep Time, read whether Constant Sweep Time is currently enabled, or read the
Constant Sweep Time length.

24.3.1

Input Parameter Block for SCVREQ 1

For this function, the parameter block has a length of two words.

24.3.2

Disable Constant Sweep Mode

To disable Constant Sweep mode, enter SVCREQ function #1 with this parameter block:

address

address + 1

ignored

24.3.3

Enable Constant Sweep Mode

To enable Constant Sweep mode, enter SVCREQ function #1 with this parameter block:

address

address + 1

0 or timer value

Note:

If the timer should use a new value, enter it in the second word. If the timer value should not be
changed, enter 0 in the second word. If the timer value does not already exist, entering 0 causes
the function to set the OK output to OFF.

24.3.4

Change the Constant Sweep Time

To change the timer value without changing the selection for sweep mode state, enter
SVCREQ function #1 with this parameter block:

address

address + 1

new timer value

24.3.5

Read the Constant Sweep State and Time

To read the current timer state and value without changing either, enter SVCREQ function
#1 with this parameter block:

address

address + 1

ignored

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Successful execution will occur, unless:

A number other than 0, 1, 2, or 3 is entered as the requested operation:

The sweep time value is greater than 500ms (0.5 seconds).

Constant sweep time is enabled with no timer value programmed or with an old
value of 0 for the timer.

After the function executes, the function returns the timer state and value in the same
parameter block references:

0 = disabled

address

1 = enabled

address + 1

current timer value

Example of SVCREQ 1

In this example, if contact OV_SWP is set, the Constant Sweep Timer is read, the timer is
increased  by  two  milliseconds,  and  the  new  timer  value  is  provided  to  the  CPU.    The
parameter  block  is  in  local  memory  at  location  %R0050.    Because  the  MOVE  and  ADD
functions  require  three  horizontal  contact  positions,  the  example  logic  uses  discrete
internal coil %M00001 as a temporary location to hold the successful result of the first rung
line.  On any sweep in which OV_SWP is not set, %M00001 is turned off.

Figure 349

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24.4

SVCREQ 2: Read Window Times

SVCREQ 2 can be used to read the times of the programmer communications window and
the system communications window. These windows can operate in Limited or Run to
Completion Mode.

Mode Name

Value

Description

Limited Mode

The execution time of the window is limited to 6ms. The window
terminates when it has no more tasks to complete or after 6ms
elapses.

Run to Completion
Mode

Regardless of the time assigned to a window, it runs until all tasks
within that window are completed (up to 400ms).

A window is disabled when the time value is zero.

24.4.1

Output Parameter Block for SVCREQ 2

The parameter block has a length of three words:

High Byte

Low Byte

address

Mode

Value in ms

Programmer Window

address + 1

Mode

Value in ms

System Communications Window

address + 2

must be zero

reserved

All parameters are output parameters. It is not necessary to enter values in the parameter
block to program this function.

Example of SVCREQ 2

In the following example, when enabling output %Q00102 is set, the Micro PLC CPU places
the current time values of the windows in the parameter block starting at location %R0010.

Figure 350

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24.5

SVCREQ 3: Change Programmer
Communications Window Mode

Use SVCREQ 3 to change the programmer communications window mode (Limited or Run-
to-Completion). The change occurs during the next CPU sweep after the function is called.
The time of the window cannot be changed; it is always 6ms.

SVCREQ 3 passes power flow to the right unless a mode other than 0 (Limited) or 2 (Run-to-
Completion) is selected.

The parameter block has a length of one word.

24.5.1

Changing the Programmer Communications Window
Mode

To change the programmer window, enter SVCREQ 3 with this parameter block:

High Byte

Low Byte

address

Mode

Example of SVCREQ 3

In the following example, when enabling input %I006 goes ON, the programmer
communications window is enabled and assigned a value of 6ms. The parameter block is in
reference memory location %R0051.

Figure 351

24.6

SVCREQ 4: Change System Communications
Window Mode

Use SVCREQ 4 to change the system communications window mode (Limited or Run-to-
Completion). The change occurs during the next CPU sweep after the function is called. The
time of the window cannot be changed; it is always 6ms.

SVCREQ 4 passes power flow to the right unless a mode other than 0 (Limited) or 2 (Run-to-
Completion) is selected.

The parameter block has a length of one word.

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24.6.1

Changing the System Communications Window Mode

To change the programmer window, enter SVCREQ 4 with this parameter block:

High Byte

Low Byte

address

Mode

Example of SVCREQ 4

In the following example, when enabling input %I0003 is ON the system communications
window is changed to Run-to-Completion mode. The parameter block is at location
%R0025.

Figure 352

24.7

SVCREQ 6: Change/Read Number of Words to
Checksum

Use SVCREQ 6 to read or change the number of words in the program to be checksummed.
The function is successful unless some number other than 0 or 1 is entered as the requested
operation.

24.7.1

Parameter Block Formats for SVCREQ 6

The parameter block has a length of 2 words. To read the word count, the first word of the
parameter block must contain a zero:

address

0 (read word count)

address + 1

ignored

The function returns the current word count in the second word of the parameter block.

address

address + 1

current word count

To change the word count, the first word of the parameter block must contain a one:

address

1 (change word count)

address + 1

new word count (0 to 32)

The PLC will change the number of words to be checksummed to the new value.

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Example of SVCREQ 6

In  the  example,  when  enabling  contact  FST_SCN  is  set,  the  parameter  blocks  for  the
checksum function are built.  Later in the program, if input %I0137 turns on, the SVCREQ
reads the number of words being checksummed. The parameter block for the Read function
is located at %R0150-151.  The ADD function adds 32 to the current word count in %R0151
and places the result in %R0153. The parameter block for the Change function is located at
%R00152-153.  The  second  SVCREQ  then  changes  to  the  new  word  count  specified  in
%R0153.

Figure 353

24.8

SVCREQ 7: Read or Change the Time-of-Day
Clock

Use SVCREQ 7 to read or change the time of day clock in the PLC. The data can be either BCD
or ASCII. Either 2-digit-year or 4-digit-year format is available. The function is successful
unless some number other than 0 (read) or 1 (change) is entered for the requested
operation, or an invalid data format is specified, or data is provided in an unexpected format.

24.8.1

Parameter Block Format for SVCREQ 7

For the date/time functions, the length of the parameter block depends on the data format.
The data block is either BCD or ASCII. BCD format requires 6 words; packed ASCII requires
12 words (13 words for 4-digit year). For both data types:

Hours are stored in 24-hour format.

Day of the week is a numeric value from 1 (Sunday) to 7 (Saturday).

2-Digit Year Format

4-Digit Year Format

address

0 = read time and date
1 = set time and date

address + 1

1 = BCD format
3 = packed ASCII format

81h = BCD format
83h = packed ASCII format

address + 2 to end

data

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Words 3 to the end of the parameter block contain output data returned by a read function,
or new data being supplied by a change function.  In both cases, format of these data words
is  the  same.    When  reading  the  date  and  time,  words  (address  +  2)  to  the  end  of  the
parameter block are ignored on input.

24.9

SVCREQ 7 Parameter Block Content: BCD
Format

In BCD format, each time and date item occupy one byte, so the parameter block has six
words.

24.9.1

2-Digit Year

The last byte of the sixth word is not used. When setting the date and time, this byte is
ignored; when reading date and time, the function returns 00.

Parameter Block Format:
High Byte:

Low Byte

Example:
Read Date and Time in BCD format
(Sun., July 3, 1998, at 2:45:30 p.m.)

1 = change or
0 = read

address

0 (read)

1 (BCD format)

address + 1

1 (BCD format)

month

year

address + 2

07 (July)

98 (year)

hours

day of month

address + 3

14 (hours)

03 (day)

seconds

minutes

address + 4

30 (seconds)

45 (minutes)

(null)

day of week

address + 5

06 (Friday)

24.9.2

4-Digit Year

The parameter block has six words. All bytes are used.

Parameter Block Format:
High Byte:

Low Byte

Example:
Read Date and Time in BCD format
(Sun., July 3, 1998, at 2:45:30 p.m.)

1 = change or
0 = read

address

00 (read)

81h (BCD format, 4-digit)

address + 1

81h (BCD, 4-digit)

year

address + 2

19 (year)

98 (year)

day of month

month

address + 3

03 (day)

07 (July)

minutes

hours

address + 4

45 (minutes)

14 (hours)

day of week

seconds

address + 5

06 (Friday)

30 (seconds)

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24.10

SVCREQ 7 Parameter Block Content: Packed
ASCII Format

In Packed ASCII format, each digit of the time and date items is an ASCII formatted byte.
Spaces and colons are embedded into the data to format it for printing or display. ASCII
format requires 12 words in the parameter block (13 words for 4-digit year).

24.10.1

2-Digit Year

Parameter Block Format:
High Byte

Low Byte

Example:
Read Date and Time in Packed ASCII
Format (Mon, Oct. 5, 1998 at
11:13:00pm)

1 = change or
0 = read

address

0 (read)

3 (ASCII format)

address + 1

3 (ASCII format)

year

address + 2

38 (8)

39 (9)

month

(space)

address + 3

31 (1)

20 (space)

(space)

month

address + 4

20 (space)

30 (0)

day of month

address + 5

35 (5)

30 (leading 0)

hours

(space)

address + 6

31 (1)

20 (space)

hours

address + 7

3A ( : )

31 (1)

minutes

address + 8

33 (3)

31 (1)

seconds

address + 9

30 (0)

3A ( : )

(space)

seconds

address + 10

20 (space)

30 (0)

day of week

address + 11

32 (2: Mon.)

30 (leading 0)

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24.10.2

4-Digit Year

Parameter Block Format:
High Byte

Low Byte

Example:
Read Date and Time in Packed
ASCII Format (Mon, Oct. 5,
1998 at 11:13:00pm)

1 = change or
0 = read

address

0 (read)

83h (ASCII 4 digit)

address + 1

83h (ASCII 4 digit)

year (hundreds)

year (thousands)

address + 2

39 (9)

31 (1)

year (ones)

year (tens)

address + 3

38 (8)

39 (9)

month (tens)

(space)

address + 4

31 (1)

20 (space)

(space)

month (ones)

address + 5

20 (space)

30 (0)

day of month (ones) day of month (tens) address + 6

35 (5)

30 (leading 0)

hours (tens)

(space)

address + 7

31 (1)

20 (space)

: (colon)

hours (ones)

address + 8

3A ( : )

31 (1)

minutes (ones)

minutes (tens)

address + 9

33 (3)

31 (1)

seconds (tens)

: (colon)

address + 10

30 (0)

3A ( : )

(space)

seconds (ones)

address + 11

20 (space)

30 (0)

day of week (ones)

day of week (tens)

address + 12

32 (2: Mon.)

30 (leading 0)

Example of SVCREQ 7

In the example, when called for by previous logic, a parameter  block for the time-of-day
clock is built. It requests the current date and time, then sets the clock to 12 noon using BCD
format.  The parameter block is located at location %R0300.  Array NOON has been set up
elsewhere in the program to contain the values 12, 0, and 0.  (Array NOON must also contain
the  data  at  %R0300.)    BCD  format  requires  six  contiguous  memory  locations  for  the
parameter block.

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Figure 354

24.11

SVCREQ 8: Reset Watchdog Timer

Use  SVCREQ  8  to  reset  the  watchdog  timer  during  the  sweep.    Ordinarily,  when  the
watchdog timer expires the PLC shuts down without warning.  SVCREQ 8 allows the timer
to keep going during a time-consuming task (for example, while waiting for a response from
a communications line).

CAUTION

Be sure that resetting the watchdog timer does not adversely affect the controlled process.

24.11.1

Parameter Block Format for SVCREQ 8

This function has no associated parameter block.

Example of SVCREQ 8

In this example, power flow through enabling output %Q0027 or input %I1476 or internal
coil %M00010 causes the watchdog timer to be reset.

Figure 355

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24.12

SVCREQ 9: Read Sweep Time from Beginning
of Sweep

Use SVCREQ 9 to read the time in milliseconds since the start of the sweep. The data format
is unsigned 16-bit integer.

24.12.1

Output Parameter Block Format for SVCREQ 9

The parameter block is an output parameter block only; it has a length of one word.

address

time since start of sweep

Example of SVCREQ 9

In the following example, the elapsed time from the start of the sweep is always read into
location %R0200. If it is greater than 100ms, internal coil %M0200 is turned on.

Figure 356

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