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•
If MCR bit 1 = 1, then RTS = 0, and serial transmitter is disabled
•
If MCR bit 1 = 0, then RTS = 1, and serial transmitter is enabled
If you are using the RS-485 inverted RTS driver enable mode these settings will be reversed as
follows:
•
If MCR bit 1 = 1, then RTS = 0, and serial transmitter is enabled
•
If MCR bit 1 = 0, then RTS = 1, and serial transmitter is disabled
If you are using the handshaking signals in RS-422/485 mode, the serial receiver for CTS (clear
to send) is always enabled, and the serial transmitter for RTS (request to send) is always
enabled.
The exact software method for toggling RTS will depend on your operating system. Consult your
operating system’s programming documentation for information on how to do this.
"NOTE: Many serial communication programs (e.g. Windows HyperTerminal) do not assert
RTS while transmitting. When using these programs, make sure jumper that
enables the transmitters all the time is installed. If using a multi-drop bus such as
RS485, the software will have to be modified to toggle RTS to enable the transmit
drivers.”
Interrupts
Since the CM17320HR is a PCI device, it is capable of sharing interrupts with other PCI devices.
Interrupt sharing is a normal part of PCI operation, and a required part of the PCI specification.
Note that any Interrupt Service Routines developed for the CM17320HR must be properly written
to support interrupt sharing.
The CM17320HR uses one PCI interrupt for all eight serial ports. The actual IRQ number will be
set by the CPU’s BIOS and operating system at boot time.
Since the XR17D158 has all the capabilities of a standard 16C550 UART, it supports all of the
standard serial port interrupt events. However, it will not actually generate interrupts unless the
Interrupt Enable Register has been properly programmed for each port. Supported interrupt
events include:
•
Received data available
•
Transmit buffer empty
•
Line Status Register change
•
Modem Status Register change
A detailed explanation of serial port interrupts is beyond the scope of this manual. For more
information, consult a serial port programming reference.
Note:
When the UART clock is running at a higher frequency, transmit/receive interrupts will
happen more frequently. Many operating systems can not process interrupts quickly
enough to handle this load. When developing your software, be sure to consider the
operating system’s limitations.
