Other signal modules
7.4 Position decoder module SM 338; POS-INPUT; (6ES7338-4BC01-0AB0)
S7-300 Automation System Module data
7-14 Manual, 08/2006, A5E00105505-04
Example of encoder value scaling
You are using a single-turn encoder with
2
9
steps = 512 steps per revolution (resolution/360°.)
Your configuration in
STEP 7
:
● Absolute encoder: 13 bits
● Scaling: 4 places
● Steps per revolution: 512
;
;;;
5HOHYDQWELWV
7UDQVIHUUHGELWV
'DWDGRXEOHZRUG
5HOHYDQWELWV
'DWDGRXEOHZRUG
3ULRUWRQRUPDOL]LQJF\FOLFDOO\PHDVXUHGHQFRGHUYDOXH
IWHUQRUPDOL]LQJ(QFRGHUYDOXH
5HVXOWELWVWRGLJLWVPDUNHGZLWK[ZHUHRPLWWHG
7.4.2.3 Freeze function
The freeze function "freezes" the actual encoder values of SM 338. The freeze function is
coupled to the digital inputs DI 0 and DI 1 of SM 338.
The freeze function is triggered by a signal transition (positive edge) a DI 0 or DI 1. Bit 31 = 1
(output address) identifies a frozen encoder value. You can freeze one, two or three encoder
values using one digital input.
Enable the freeze function by setting the corresponding parameters in
STEP 7
.
To allows their event-triggered evaluation, the encoder values are retained until the freeze
function is terminated.
Terminating the freeze function
The freeze function must be terminated separately at each encoder input. You acknowledge
the function in the user program by setting bit 0, 1 or 2 of the relevant channel by setting the
STEP 7
operation T PAB "xyz."
The acknowledgement resets bit 31 of the corresponding encoder value, and initiates a
refresh of the encoder values. You can freeze the encoder values again after you cleared the
ACK bit at the output address of the module.
In isochronous mode, the acknowledgement is processed at the time T
o
. From this point on,
you can freeze the encoder values again by setting the digital inputs.
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