ZyXEL U-1496S Plus User Guide - Page 62

Ten, Synchronous Operation

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strings. Since new computers are much faster and there is an increasing use of serial port chips with internal buffers like the 16550A UART, the computer's speed is less of a problem now. The default setting for throughput averaging is disabled. This will reduce data delay and increase throughput in Unix applications. You can enable throughput averaging by setting S42 bit 1 to 1. HINT FOR HIGH-SPEED OPERATION The communication software tends to lose incoming serial data when it is doing block disk data transfers, because the hard disk interrupt priority level is usually higher than that of the serial port interrupt in the computer. The communication software can do a hardware flow control during disk data transfer to prevent this. On some computers, a change of resolution or of the number of colors may result in higher speeds, because less time is used to transfer data to the video buffer. Choice of an efficient assembly coded communication software is also very important. When using communication software, use a simple protocol without error control (modem has done this job) such as YModem-G and ZModem. Software with complicated protocol handling will slow down its speed in handling serial data. FLOW CONTROL This feature refers to stopping and restarting the flow of data into and out of the modem's transmit and receive data buffers. Flow control is necessary so that a device (computer or modem) does not receive more data than it can handle. The U-1496 series modems provide two kinds of flow control methods. Hardware CTS/RTS Flow Control This is a bidirectional flow control where CTS and RTS are RS-232 signals which must be available on your computer. When the modem's transmit buffer is almost full, the modem will drop CTS to signal DTE that it cannot take any more data. Turn ON the CTS to notify DTE that it can keep sending data to the modem. At the computer software side, when the receive buffer of the software is almost full, it will drop RTS to signal the modem to stop sending data to DTE. Turn ON the RTS and the modem will start sending data again to DTE. In asynchronous fullduplex applications, the U-1496 always responds to the RTS signal as a flow control signal. The U-1496 defaults automatically to this hardware flow control setting and it is a better choice. Software XON/XOFF Flow Control It is a bidirectional flow control. XON and XOFF character defaults are decimal 17 and 19. These can be changed by modifying S-Registers 31 and 32. Both modems and DTE will treat XOFF as a signal to stop transmitting data, and will treat XON as a signal to restart sending data. Modems will not send these characters received from the local DTE to the remote modem. Chapter Ten - SYNCHRONOUS OPERATION This chapter gets you started using the U-1496 series modem for synchronous operation. Use the U-1496 as a synchronous modem when it is connected to a synchronous computer or

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strings.
Since new computers are much faster and there is an increasing use of serial port chips with
internal buffers like the 16550A UART, the computer's speed is less of a problem now. The
default setting for throughput averaging is disabled. This will reduce data delay and increase
throughput in Unix applications. You can enable throughput averaging by setting S42 bit 1 to 1.
HINT FOR HIGH-SPEED OPERATION
The communication software tends to lose incoming serial data when it is doing block disk data
transfers, because the hard disk interrupt priority level is usually higher than that of the serial port
interrupt in the computer. The communication software can do a hardware flow control during
disk data transfer to prevent this.
On some computers, a change of resolution or of the number of colors may result in higher
speeds, because less time is used to transfer data to the video buffer.
Choice of an efficient assembly coded communication software is also very important. When
using communication software, use a simple protocol without error control (modem has done this
job) such as YModem-G and ZModem. Software with complicated protocol handling will slow
down its speed in handling serial data.
FLOW CONTROL
This feature refers to stopping and restarting the flow of data into and out of the modem's
transmit and receive data buffers. Flow control is necessary so that a device (computer or
modem) does not receive more data than it can handle. The U-1496 series modems provide two
kinds of flow control methods.
Hardware CTS/RTS Flow Control
This is a bidirectional flow control where CTS and RTS are RS-232 signals which must be
available on your computer.
When the modem's transmit buffer is almost full, the modem will
drop CTS to signal DTE that it cannot take any more data. Turn ON the CTS to notify DTE that it
can keep sending data to the modem. At the computer software side, when the receive buffer of
the software is almost full, it will drop RTS to signal the modem to stop sending data to DTE.
Turn ON the RTS and the modem will start sending data again to DTE. In asynchronous full-
duplex applications, the U-1496 always responds to the RTS signal as a flow control signal. The
U-1496 defaults automatically to this hardware flow control setting and it is a better choice.
Software XON/XOFF Flow Control
It is a bidirectional flow control. XON and XOFF character defaults are decimal 17 and 19. These
can be changed by modifying S-Registers 31 and 32. Both modems and DTE will treat XOFF as
a signal to stop transmitting data, and will treat XON as a signal to restart sending data. Modems
will not send these characters received from the local DTE to the remote modem.
Chapter Ten -
SYNCHRONOUS OPERATION
This chapter gets you started using the U-1496 series modem for synchronous operation. Use
the U-1496 as a synchronous modem when it is connected to a synchronous computer or