Rockwell Automation 2755 AtomScan Bar Code Reader - Manual (Page 51)

5–6 Configuring Your Reader
Publication 2755-6.9
Host Protocol Parameters
•
Protocol. Protocols define the sequence and format in which
information is transferred between devices. The protocol options
are listed in the following table.
Parameter Description
Point-to-Point
Has no address and sends data to the host (RS-232) whenever it is available and
without any request or handshake from the host.
Point-to-Point with
RTS/CTS (Request-to-
Send/Clear-to-Send)
Used only with RS-232. This is a simple handshaking protocol that allows a device
to initiate data transfers to the host with an RTS (request-to-send) transmission. The
host, when ready, responds with a CTS (clear-to-send) and the data is transmitted.
CTS and RTS signals are transmitted over two dedicated wires (pins 6 and 10) as
defined in the RS-232 standard.
Point-to-Point with
XON/XOFF
(Transmitter On/Off)
Used only with RS-232. This selection enables the host to send a single byte
transmission command of start (XON) or stop (XOFF). If an XOFF has been
received from the host, data will not be sent to the host until the host sends an XON.
During the XOFF phase, the host is free to carry on other chores and accept data
from other devices.
Point-to-Point with
RTS/CTS &
XON/XOFF
Used only with RS-232. It is a combination of Point-to-Point with RTS/CTS and
Point-to-Point with XON/XOFF.
Polling Mode D
Like Point-to-Point, Polling Mode D requires a separate connection to the host; but
unlike Point-to-Point, it requires an address and must wait for a poll from the host
before sending data. When in Polling Mode D, an address of 1 is automatically
displayed on the configuration screen. However, during transmission, a 1C hex poll
address (FS) and a 1D hex select address (GS) are substituted for the 1.
Multidrop ➀
Similar to Polling Mode D except that a unique poll address and select address are
required for each multidrop device, and only one host port connection is needed for
up to 50 devices. Requires a concentrator or controller using RS-485
communications. When Multidrop is selected, the protocol characters for RES, REQ,
etc. are assigned automatically.
User Defined
Used only with RS-232. ASCII characters can be assigned as an address and as
protocol commands (RES, REQ, EOT, STX, ETX, ACK, and NAK). User Defined is
necessary when a new protocol must be defined to match a specific host protocol.
When User Defined is selected, the displayed protocol commands match those of
the previously selected protocol. User Defined is considered to be in a polled mode
only if an address has been assigned. The address can be any ASCII character
except NUL
➁ .
User Defined Multidrop
Used when connecting to a concentrator or other device that does not match
standard Multidrop protocol. Any single character (01 hex to 7E hex) in the ASCII
table can be assigned as the address character. The character chosen is used as
the poll character and the subsequent ASCII character becomes the select
character. For example, if a ^A (01 hex) is selected as the address, ^B (02 hex)
becomes the select address that the host will use in sending host select commands.
➀
Once the reader is configured for Multidrop, a terminal connected to the auxiliary RS-232 pins or a
default procedure must be used to access the configuration menus again (although serial
commands will continue to function).
➁
For example a simple ACK/NAK protocol can be developed by first selecting Point-to-Point, then
User Defined, and then assigning characters to ACK and NAK commands. First scroll to the
following command:
HOST PROTOCOL --> PROTOCOL --> USER DEFINED--> ACK = --> Press [^F] by holding
down the Control key while pressing the F key, and then press [CR] to see the following:
HOST PROTOCOL --> PROTOCOL --> USER DEFINED --> ACK = ^F