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null modem for testing
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ace(7) Miscellaneous Information Manual ace(7) NAME
ace - Serial communications interface SYNOPSIS
controller ace0 at * slot ? vector aceintr DESCRIPTION
The ace serial line controller provides a serial communications interface on DEC 2000, AlphaStation, and AlphaServer platforms. The serial communications ports that are controlled by ace adhere to the RS-232 standard and can operate at rates from 50 to 115200 baud (see tty(7)). These communications ports support serial-line printers, modems, and terminals. In alternate console configurations (that is, no graphics head), the terminal to be the system console must be connected to the port that is mapped to /dev/tty00. (See ports(7) for information about mapping AlphaStation and AlphaServer port labels to device pathnames.) Cur- rently, some processors that use the ace driver limit the serial console port to 9600 baud, 8-bit, no parity and no modem support. However, some processor consoles do support baud rates other than 9600 baud and allow the use of modems as console devices. Consult your hardware documentation to determine the type of console support your system provides. The driver for the ace interface supports hardware flow control using the Request to Send (RTS) and Clear to Send (CTS) signals. When hardware flow control is enabled, the flow of input data is controlled by the RTS signal and the flow of output data is controlled by the CTS signal. If the CTS signal is off, the driver suspends output to that line until the CTS lead is reasserted. Likewise the driver turns off the RTS lead to tell the device connected to the line to stop sending data as a result of congestion on the host side. When the condi- tion clears, the driver turns on the RTS lead to tell the device to resume sending data. The DCD (carrier detect) timer value defaults to 2 seconds. This value may be changed if your modem hardware requires a different value. the change can be made in the /etc/sysconfigtab file as follows: ace: dcd_timer=n where n is the time interval in seconds, and can be set to 0 (no timeout), 1, or 2 seconds. Alternatively, you can use the sysconfig com- mand to set the same time interval option as follows: # sysconfig -r ace dcd_timer=[n] If you use the sysconfig command, the value will not be preserved when the system is rebooted. To preserve the setting, put the entry in the /etc/sysconfigtab file NOTES
If you are using the alternate system console to perform kernel debugging, you must change the kdebug entry in the /etc/remote file to use /dev/tty01; when the kernel is running in debugging mode, no other application can use the port. See Kernel Debugging for information on setting up your system for kernel debugging. RESTRICTIONS
Unless alternative specifications are stated in your system hardware documentation, data communications equipment attached to the console serial port in alternate console configurations must be set to 9600 baud, 8-bits, no parity. If a serial console is being used, /dev/tty00 cannot be opened by another process. The ace driver enforces this restriction. Baud rates greater than 38400 are not supported on the two primary serial ports on the DEC 2000 system. However, if you use an ISA serial or modem card that is capable of communicating at the higher rates, the higher rates are supported. FILES
console terminal local terminal local terminal RELATED INFORMATION
MAKEDEV(8), console(7), devio(7), modem(7), ports(7), tty(7) Kernel Debugging System Administration delim off ace(7)
