VISUAL 100 - Synchronization

VISUAL TECHNOLOGY INCORPORATED, 540 MAIN STREET, TEWKSBURY, MA 01876
Exit Alternate Keypad Mode, ESC >
This sequence causes the terminal to exit Alternate Keypad mode.
5.4 SYNCHRONIZATION
If the Auto XON/XOFF feature is enabled, the terminal will generate the XON/XOFF
synchronization codes to assure no data transmitted from the host is lost. The terminal will
generate the XOFF code (DC3) in response to the following conditions:
• Receive FIFO buffer becomes almost full.
• NO SCROLL key depressed.
• CTRL S keys depressed.
• Buffered printer interface FIFO almost full.
The terminal will generate the XON code (DC1) in response to the following conditions:
• Receive FIFO buffer becomes almost empty.
• NO SCROLL key depressed again.
• CTR L Q keys depressed.
• Buffered printer interface FIFO al most empty.
If the Auto XON/XOFF feature is not enabled, the terminal will generate the XOFF code
only when CTRL-S is depressed, and generate the XON code only when CTRL-0 is
depressed.
The Auto XON/XOF F feature assures no transmitted data will be lost, only if the host
supports XON/XOFF and responds in a timely manner. If the host does not respond in a
timely manner th~ Fl FO buffer may be overrun causing lost data.
To determine if the buffer will overrun, the following formulas should be used.
No. of characters to overrun buffer= 32-[3x(receive rate/X-mit rate)]
Time to respond to XOFF= No. of characters to overrun buffer x(bits per character +2)/
receive rate
Example:
The VISUAL 100 is transmitting 8 bit characters at 1200 baud and receiving at 9600 baud.
The terminal sends XOF F to the host to stop transmission. In this case, the time for the
host to respond to XOFF is:
No. of characters to overrun buffer= 32-[3x(9600/1200)] =8
Time to respond to XOF F= 8x(8+2)/9600= 0.008333 seconds.
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