DS71-MD4 Serial host and 56k Modem
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Stop Bits
The Stop Bits are used to signal the end of communication for a single packet. Since the data is clocked
across the lines and each device has its own clock, it is possible for the two devices to become slightly
out of sync. Therefore, the stop bits not only indicate the end of transmission but also give the computers
some room for error in the clock speeds. The more bits that are used for stop bits, the greater the
lenience in synchronizing the different clocks, but the slower the data transmission rate.
Select “Stop Bits” the DS displays the following: Default is 1.
Parity
Parity is a simple form of error checking used in serial communication. For even and odd parity, the
serial port will set the parity bit (the last bit after the data bits) to a value to ensure that the transmission
has an even or odd number of logic high bits. For example, if the data was 011, then for even parity, the
parity bit would be 0 to keep the number of logic high bits even. If the parity was odd, then the parity bit
would be 1, resulting in 3 logic high bits. This allows the receiving device to know the state of a bit so as
to enable the device to determine if noise is corrupting the data or if the transmitting and receiving
devices' clocks are out of sync.
With no parity selected, it's assumed that there are other forms of checking that will detect any errors in
transmission. No parity also usually means that the parity bit can be used for data, speeding up
transmission. In modem-to-modem communication, the type of parity is coordinated by the sending and
receiving modems before the transmission takes place.
Select “Parity” the DS displays the following: Default is None.
XON/XOFF
For a simple communication between modems three connected lines are needed: TX, Rx, and Ground.
For the data to be transmitted, both sides have to be clocking the data at the same baud rate. While this
method is sufficient for most applications, it is limited in being able to respond to problems such as the
receiver getting overloaded. This is where serial handshaking can help. XON/XOFF is software data
flow communications protocol for controlling the flow of data between Baytech and other devices.
Baytech units will send an XOFF character when it can't take any more data and when it can once again
take more data, will send an XON character to the transmitter.
Select “Xon/Xoff” the DS displays the following, Default is Off:
" 5 " ......1
" 6 " ......2
" 7 " ......3
" 8 " ......4
Enter Select :
" 1 " ......1
" 2 " ......2
Enter Select :
" None " ......1
" Even " ......2
" Odd " ......3
Enter Select :
