User`s manual

CHAPTER 5
RS-232C/422/485 INTERFACING
5-3
MEMORY BUFFERS
The ESTeem has a 2020 byte buffer on the TRANSMIT
SIDE (outgoing data) and a 2020 byte buffer on the
RECEIVE SIDE (incoming data).
Transmit Buffer
The Outgoing data buffer will hold two data blocks
before the ESTeem will enable its RS-232C
hardware/software control on data coming into the
modem if the network is busy. A data block in this
example is a block of data that is defined by the
PACKLENGTH or SENDPAC character which ever
occurs first.
Therefore, if PACKLENGTH = 10 the modem will
accept a maximum of 20 bytes before it enables its
hardware/software handshake line (two 10 byte packets).
In another example, if PACKLENGTH = 1010 but the
data block is terminated by the SENDPAC character
before the input buffer reaches the full 1010 bytes, the
buffer will still hold only two data blocks if the network
is busy.
In order to utilize the 2020 bytes storage for small data
packets (bar code readers, etc.), program the modem
using the following guidelines:
PACKLENGTH = 1010 SENDPAC = 255
TERMC = ON TERMT = 10
Note: Set the TERMT time greater than the pause
between data bursts.
By programming the above parameters the ESTeem will
buffer the incoming data packets and automatically
transmit the data when the 1010 byte buffer is filled or
the TERMT time limit is met. This will allow the
customer to use two blocks of 1010 or 2020 bytes before
the modem enables the respect hardware/software
control.
Receive Buffer
If the device that the receiving ESTeem is outputting data
to, enables its respective hardware or software control,
the modem will store 2020 bytes of data before flow
controlling off the transmitting ESTeem.
REQUEST TO SEND/CLEAR TO SEND
A software switch, RTS_CTS (on/off), is provided in the
ESTeem for operation of the Request to Send (RTS) pin 4
and Clear to Send (CTS) pin 5 when Hardware Flow
control is not necessary or available, but the RTS/CTS
lines are required. When the users device raises the RTS
line (Pin 4) the ESTeem will assert the CTS (Pin 5) in
response. This feature is used to have the ESTeem
emulate a standard phone modem, but can NOT be used
a method of flow control.
When the RTS_CTS software switch is ON,
HARDWARE FLOW CONTROL can NOT be enabled in
the ESTeem.
The factory default setting for this switch is OFF.
DATA TERMINAL READY (DTR)
A software switch, DTR_ENAB (ON/OFF) is provided in
the ESTeem for monitoring the status of a device
connected to pin 20 of the RS-232C connector. The
factory default setting is OFF. When this command is
enabled the ESTeem will monitor the DTR signal on pin
20. If the DTR line being supplied to the ESTeem, from
the user, is at a SPACE (high) condition then the
ESTeem is enabled. If the DTR line is at a MARK (low)
condition then the ESTeem is disabled.
This signal is normally used by the ESTeem modem as
an indication that connection is made to a device that is
on line and ready to transmit/receive data.
Also note that if DTR command is enabled, and the line
is disabled then the ESTeem will perform a "Disconnect"
if connected. DTR enabled also turns on Carrier Detect
(pin 8) if the ESTeem is "Connected" to another
ESTeem, Carrier Detect will go off if the ESTeem is
"Disconnected".