User's Manual

MDS 05-6399A01, Rev. D MDS Master Station 39
• Vmin - Receive Buffer Size - The minimum number of data bytes that will be buffered by the seri-
al port before handling of the data to be processed by the terminal server. (255 = DEFAULT).
• Vtime - Receive Inter-Byte Timeout - The amount of time between bytes of data on the serial port
(in multiples of 1 millisecond), that indicate the end of a serial message ready to be processed by
the terminal server. (100 = DEFAULT)
Note
Vmin and Vtime setting only have an effect when the serial port is not being used an SD
payload or diagnostics (DLINK) port,
Terminal Server Settings
When configuring a serial port that will be used as a terminal server the VMIN and VTIME settings need
additional explanation. As described above VMIN is a number describing bytes that are received from the
interface, while VTIME is in 100
th
s of a second (100 milliseconds) intervals. They act together to control
serial data collection and transmission as described below:
• VMIN == 0; VTIME == 0: The terminal server will continuously read to see if a byte if data is
available and process each byte.
NOTE
While this is a valid mode in most cases this causes a high processing load on the device that may impact
performance of other operations of the device.
• VMIN > 0; VTIME == 0: The terminal server waits to process data until at least VMIN bytes of
serial data are received.
• VMIN == 0; VTIME > 0: If serial data is received, the terminal server will continuously read the
number of bytes available until
• VTIME has elapsed then process the data
• VMIN > 0; VTIME > 0: Once an initial byte of input becomes available the terminal server waits
until the MIN bytes have been read, or when the inter-byte timeout expires. The timer is restarted
after each further byte is received and because the timer is started only after the initial byte is re-
ceived, at least one byte will be read
Serial Hardware Flow Control - When port is not being used as a SD payload or SD
diagnostics (DLINK) port:
Hardware Flow Control: When operating in CTSKEY mode, all serial ports in the data path are required
to be set to the same baud rate, and that VMIN and VTIME remain at the defaults for serial data packets
less than or equal to 255 bytes. For serial packets over 255 bytes it is recommended that a cts-delay time
of at least 90ms be used to account for the VTIME delay of the over-the-air sending unit.
Hardware Flow Control Modes - When port is not being used as a SD payload or
SD diagnostics (DLINK) port:
1. DCE
• CTS follows RTS after a programmable CTS delay.
• If the unit’s input buffer approaches a full condition it can deassert CTS regardless of state of RTS.
2. CTSKEY
• Based on legacy MDS devices including TransNET, the device will act similar to a DTE but will
provide signaling on the CTS line instead of the RTS line.
• When the first character of a transmission is ready to be sent to the serial port, the unit shall assert
CTS and delay for CTS delay time expiration before outputting the first character.