Plc Variable; Description Of The Blocks; Requirements Of The Plc Programm - Siemens SINUMERIK 840D sl Commissioning Manual

08/2005

5.3 PLC variable

5.3.1

Description of the blocks

In the PLC interface area DB19. Byte10 is provided for key selection. Here, the
PLC can select one key between 50 and 254 directly.
(Keys 1 to 49 are reserved for Siemens, keys 50-254 are specific PLC keys.)
Note
In M:N mode, the area for the 2nd HMI interface is DB19.Byte60;
See also: Description of Functions B3 "Interfaces in DB19 for M:N".
Acknowledgment
An HMI system acknowledgment is divided into two steps:
1. In the first step, the HMI software transfers the control information 255 to
DB19.Byte10.
2. In the second step, the actual acknowledgment takes place on the PLC in
which DB19.Byte10 is cleared.
This is necessary in order that, despite the lack of synchronism between the HMI
and the PLC, the same key code transferred twice in immediate succession can be
detected by the HMI. This defined virtual key activation enables the HMI to identify
every PLC key sequence uniquely. The control information is of no significance to
the PLC program (transparent) and must not be changed.
Next key input
If the transfer byte is set to 0, the PLC program can specify a new key. The current
key request is processed in parallel in the HMI system. The request leads to a
switchover to the corresponding task or initiates a state/action command in the
current task (configured in keys.ini).
Fault
If the task switchover cannot be executed, the operator interface will send a
message to indicate this.
5.3.2

Requirements of the PLC programm

A new request can only be set if the HMI system has acknowledged the previous
request (0 in the interface). If the PLC program is deriving the key from an MCP
key or from another source, it must provide sufficient intermediate storage for the
key to ensure that no data is lost if the key is pressed very quickly.
© Siemens AG, 2005. All rights reserved
SINUMERIK 840D sl/840D/840Di/810D HMI Installation and Start-Up Guide (IAM) – 08/2005 Edition
Expanding the Operator Interface (BE1)
5 Configuring OP Hotkeys and PLC Keys
BE1/5-129