 |
Status Message Specifications
Header Information
JBM Electronics Co. has developed a set
of headers to provide a mechanism for bridging the different characteristics between the "frame-type"
data of a polled legacy protocol and the "stream-type" data of a TCP/IP connection. The headers pass
information between a customer-developed application and the Gateway. The header is stripped before
the data is sent to the serial device.
We provide an expanded theory of operation,
examples of header (status) processing logic and example code which can be used to as a guide when
adding support for our headers to a TCP application. This code will simplify the effort necessary
to support the headers. The available information is:
Overview
The status messages are used by a TCP/IP
application to obtain specific information about certain low-level information at a remote serial
interface (where supported), or to control certain low-level operations. For example, the
application may initiate/terminate polling, detect line activity and a variety of error conditions.
All of the status messages conform to the following format:
| Byte |
Bit(s) |
Field |
Description |
| 0 |
7-0 |
Format ID |
Identifies the status format. The following
values are defined:
All other values are Reserved. |
| 1 |
7-0 |
Version ID |
Identifies the version. The following
values are defined:
All other values are Reserved. |
| 2-n |
- |
Status |
Content is both version and Port Controller
implementation dependent, and take on different forms depending on whether or not the status
message is a request or a response.
| Version
1 - Request format |
| Byte |
Bit(s) |
Field |
Description |
| 2 |
7-4 |
Reserved |
Always zeroes. |
| 3-0 |
Command
Request ID |
Identifies the type of status request being commanded.
The following values are defined:
| 0001 |
- Line Status Request. |
All other values are Reserved. |
| 3 |
7-0 |
Reserved |
Always zeroes. |
| Versions
1 & 2 - Response format |
| Byte |
Bit(s) |
Field |
Description |
| 2 |
7-5 |
Reserved |
Always zeroes. |
| 4 |
Solicited/Unsolicited
Indicator |
Indicates whether
or not the status is in response to a previous request, or has been generated as an unsolicited status
delta. The following values are defined:
| 1 |
- Solicited Response. |
| 0 |
- Unsolicited Response. |
|
| 3-0 |
Line Status
Indicator |
Indicates the current state of the serial
interface. The following values are defined:
| 0100 |
- Line senses 'activity' (polling). |
| 0010 |
- Line has physical connection. |
All other values are Reserved. |
| 3 |
7-0 |
Input Message
Status Indicator |
Indicates status relating to data received by the
serial interface. The following values have been defined:
Poll-Select Protocol
| 0000 0001 |
- Message failure: Parity/BCC error. |
| 0000 0010 |
- Message failure: Timed out during receive. |
| 0000 0100 |
- No response to Poll. |
| 0000 1000 |
- Garbled response. |
| 0001 0000 |
- DCD time-out. |
| 0010 0000 |
- Device resumed responding to Polls. |
Bisync (Contention) Protocol
| 0000 0010 |
- Negative confirmation to message that
was discarded. |
| 0000 1000 |
- Received bad text, NAK count exceeded. |
| 0001 0000 |
- Receiver timed out waiting for text. |
| 0010 0000 |
- NAK count exceeded for transmitted
text, message discarded. |
| 0100 0000 |
- No response to line bid, message
discarded. |
Bisync (3270) Protocol
| 0000 0001 |
- Received 'Intervention Required'. |
| 0000 0010 |
- Negative confirmation to message that
was discarded. |
| 0000 0100 |
- Received 'Device Busy', pending
'Device End'. |
| 0000 1000 |
- Received bad text, NAK count exceeded. |
| 0001 0000 |
- Receiver timed out waiting for text. |
| 0010 0000 |
- NAK count exceeded for transmitted
text, message discarded. |
| 0100 0000 |
- No response to line bid, message
discarded. |
| 1000 0000 |
- 'Device End' received. |
All other values are reserved. |
| Version
2 - Request Format |
| Byte |
Bit(s) |
Field |
Description |
| 2 |
7-4 |
Command
Request ID |
Identifies the type of status request being commanded.
The following values are defined:
| 0001 |
- Line Status Request. |
| 0010 |
- Terminal Status Command: Begin Polling. |
| 0100 |
- Terminal Status Command: Stop Polling. |
All other values are Reserved. |
| 3-0 |
Reserved |
Always zeroes. |
| 3 |
7-0 |
Reserved |
Always zeroes. | |
Status Message Operations
Status messages may be either unsolicited, where
the remote serial interface simply generates a status to report a change in state, or solicited, involving
a simple conversational request-response exchange initiated from the TCP/IP application.
When using the TYPE 2 Extended Header, the Poll
Code fields may be used to identify a specific logical channel on the remote serial interface.
If the fields are set to zero (by default when using the TYPE 1 header), the status reported is that
of the physical device in general.
 Printer friendly
(Adobe Acrobat) version of this document.
If you have any questions on the headers, please e-mail us at:
support@jbmelectronics.com
|
|
|
 |
|
