20
13-
01
36
Commands
If the status is FFh (command detected), the second byte of the response also
corresponds to the second byte of the command call-up. In the actual response
(status not FFh), the second byte contains the parameters for the response, i.e.
the number of words in the response and the channel used to transmit the
response. After a read command is issued, a response with the status 00 in the
"Word count" response parameter then contains the number of words in the
response telegram (which is also the command call-up). The number of words in
a response to a write command is 0000b because the response only contains the
status and not (useful) data. Here, the second byte of the response is not the
same as the second byte of the command call-up. With read only code
commands, the word count in the response is always 0000b. 3 responses are
issued for commands to all connected R/W heads (channel = 111b): The first
response (status = FFh) is followed up by 2 other responses that contain the
status of the individual channels. The "Channel" parameter in the response
telegram contains the number of the relevant channel (001, 010).
If new response data is available, the previous data is overwritten. The
configurable data hold time value defines the minimum duration that old data is
retained before it may be overwritten with new data. The default setting for the
timer value is 0.
New commands may only be issued to the device once the answer was retrieved
from the previously issued command.
Enhanced
commands are executed repeatedly as long as the commands remain
in the output data field. Execution stops only when a new command for the
channel on which the
Enhanced
command was executed is written to the output
data field.
When the system is switched on, the value on the reply counter is also 00h. This
value increases every time the response data field is modified. This also applies if
the status changes to FFh or from 00h to 05h (with
enhanced
commands: data
carrier leaves the detection range).
In the event of an overrun, the counter skips from FFh to 01h.
7.3.4
Command types
When using commands, a distinction is always made between the two command
types
single mode
and
enhanced mode
.
Single mode
The command is executed once. A response is issued immediately.
Enhanced mode
The command remains permanently active until it is interrupted by the user or by
an error message. A response is issued immediately.
The command remains active after the response is issued. Data is only
transferred if read/write tags change. Read/write tags are not read twice. If a
read/write tag leaves the read range, the status '5' is output.
