User Manual Part 1

CHAPTER 5
RS-232C/422/485 INTERFACING
Revised: 8 Oct 03 5-3 EST P/N AA104
MEMORY BUFFERS
The ESTeem has a 4000 byte buffer on the TRANSMIT SIDE (outgoing data) and a 4000 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 flow 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 input a maximum of 20 bytes before it enables its hardware/software handshake
line (two 10 byte packets). In another example, if PACKLENGTH = 2000 but the data block is terminated by the SENDPAC
character before the input buffer reaches the full 2000 bytes, the buffer will still hold only two data blocks if the network is busy.
In order to utilize the 2000 bytes storage for small data packets (bar code readers, etc.), program the modem using the following
guidelines:
PACKLENGTH = 2000 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 2000 byte buffer is filled or the TERMT time limit is met. This will allow the customer to use two blocks of 2000 or 4000
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 4000 bytes of data before flow controlling off the transmitting ESTeem.
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.