Quatech Asynchronous Communications Adapter for PCI bus DSCLP/SSCLP-100 User Manual

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Quatech Asynchronous Communications Adapter for PCI bus DSCLP/SSCLP-100 User Manual Manual pdf 13 page image

4.4.2 Clock Rate MultiplierA standard RS-232 serial port operates at a clock speed of 1.8432 MHz.In order to achieve higher data rates, Quatech Enhanced Serial Adapters canoperate at two times, four times or even eight times this standard clock speed.This is controlled by the clock rate multiplier bits in the Options Register.Software can determine the UART clock frequency by reading the clockrate multiplier bits RR1 and RR0 in the Options Register as shown in Figure 11.RR1 and RR0 can be set by writing to the Options Register if the X2 and X4jumpers (J4-J5) are all removed. This card has the 16550 UART. If one of thesejumpers is applied, the RR1 and RR0 bits are forced to the appropriate value.Reading the Options Register will always return the clock rate multiplier at whichthe board is operating.921.6 kbaud14.7456 MHzX8*11460.8 kbaud7.3728 MHzX401230.4 kbaud3.6864 MHzX210115.2 kbaud1.8432 MHzX1(default)00Maximum DataRateUART ClockFrequencyClock RateMultiplierRR0RR1Figure 11 --- Rate Register bit definition*x8 mode is only accessable via sotware controlAt powerup and reset, the Options Register is initialized to 0. TheDSCLP-100 will thus powerup in the x1 mode with software control of the clockrate multiplier enabled as long as the X2 or X4 jumpers are not installed.Software can control high baud rates through a combination of changingthe clock rate multiplier and the UART baud rate divisor. For example, a baudrate of 230.4 kbps could be achieved by setting the clock rate multiplier to X2mode (or by applying the X2 jumper) and setting a software application for 115.2kbps.13 DSCLP/SSCLP-100 User's Manual