Page 37 of 101
DWG ID: 181-0101-00A
Date: 2003-09-26
9.5.1
Poll Mode Protocol Description
The POLL mode is generally used in system applications that implement a polled-
response protocol between a central site (Control Site) and one or more remote locations
(Remote Site). The POLL mode is similar to the TUP mode since it uses a data
transparent broadcast mode and a packet protocol with CRC-16 error checking to insure
the integrity of the received data. All ASCII characters (hex 00 through FF) can be
transmitted and received. The POLL mode differs from TUP mode by allowing an
application program to address specific locations without changing any modem
parameters. All data sent by the application program at the central sit must begin with the
address (POLLID) of the intended remote modem. When any remote modem receives
data from the radio, the data is checked for errors and the received POLLID is compared
with its own POLLID. If they match, the POLLID is stripped and the data that follows is
sent to the serial port. All data received by the central site from the remote location will
arrive with the POLLID of the remote site automatically attached to the beginning of the
data.
It is the responsibility of the application program to (1) address data to be sent to the
remote sites, (2) determine if the data was received, and (3) recognize responses that
contain the remote site's POLLID and data.
Digipeating is not allowed
9.5.2
Poll Mode Operation
9.5.2.1
Commands Used
Each modem is set up differently depending upon whether it is to be a Control modem or
a Remote modem.
9.5.2.1.1
Control Site
Control Site Configuration
- The POLLID command in the Control modem must be set
to 0000 and the INTFACE command must be set to POLL. (See "Entering POLL Mode"
below.)
Control Site Transmit Format
- All data sent to the Control modem via the RS-232
serial port
must
begin with a POLLID (four-digit remote address between 0001-9999)
and be followed immediately by the poll data. The data sent by the application to the
Control modem must contain less than PACLEN bytes. If the poll data contains more
characters than allowed by the setting of the PACLEN command, the data will be
fragmented and multiple packets will be formed and transmitted by the modem. These
additional packets will contain
only
the balance of the data received by the modem. Since
these packets do not begin with a POLLID, they will be ignored by all Remote modems.
