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Hardware Installation
Modem Configuration
3. Data bits that holds the data to be transferred
4. Parity bit used for error checking and
5. 1 or 2 Stop bits that indicates the end of the data message.
An example of 10-bit communication format is 9600 Baud, 8 Data bits, None Parity and 1 Stop bit. For instance, 1
Start bit + 8 Data bits + 0 Parity bit + 1 Stop bit = 10 bits. Ex. 1
An 11-bit format example is 9600 Baud, 8 Data bits, Even Parity and 1 Stop bit. For instance, 1 Start bit + 8 Data bits
+ 1 Parity bit + 1 Stop bit = 11 bits. Ex. 2
Modem error correction protocols do not use the parity method for error detection/correction so transmitting a parity
bit with every byte just adds 10% to the data that gets transmitted over the line. Electing to not use the Parity bit
does allows for greater bit transmission over the phone lines. This means faster Modem-to-Modem and Modem-to-
Service Provider connection rates. The VT-MODEM-4 does not use the parity bit over the phone line. This means
the Parity bit is stripped out when 11-bits are used and added back in at the receiving modem.
Along with the decide advantage of faster connection speeds there are a few limitations. The VT-MODEM-4 cannot
respond to AT commands at the port parameters list in Table 1 although either modem will transfer data correctly
with most port parameters.
PORT PARAMETERS
Since there is a limitation with 11-bit port parameters, Sixnet asks that the following suggestion be taken when
connecting the VT-MODEM-4 to a device that requires one of the port parameters in Table 1. When dialing with a
computer at the Host end of the connection, configure the host end for 8 Data bits, None parity, 1 Stop bits. In
addition, for connecting with a 3rd party device on the remote end, configure the remote device and the modem
connected to the remote device's required parameters (8 Data bits, even parity, 1 stop bit in the example below).
The VT-MODEM-4 must be configured correctly to handle the port parameters correctly as well. The Set Modem
Wizard included free with your modem will configure these AT commands, but if you wish to enter them manually
use the following table to send the correct AT commands to the modem.
VT-MODEM-4 Hardware Guide
RESPOND TO AT COMMANDS
8,E,1
8,E,2
8,O,1
8,O,2
7,N,1
TRANSFER DATA
-
-
-
-
-
Table 1.
Revised 2018-12-10
Drawing No. LP1087-A
YES
YES
YES
YES
-
2-11
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