Quatech Asynchronous Communications Adapter DSC-200/300 User Manual

Quatech Asynchronous Communications Adapter DSC-200/300 User Manual Manual pdf 17 page image

4.4.2 Clock Rate MultiplierA standard serial port operates at a clock speed of 1.8432 MHz. In order toachieve higher data rates, Quatech Enhanced Serial Adapters can operate at two times,four times, or even eight times this standard clock speed. This is controlled by theclock rate multiplier bits in the Options Register.Software can determine the UART clock frequency by reading the clock ratemultiplier bits RR1 and RR0 in the Options Register as shown in Figure 12. RR1 andRR0 can be set by writing to the Options Register if the X2, X4, and X8 jumpers (J10-J12)are all removed. If one of these jumpers is applied, the RR1 and RR0 bits are forced tothe appropriate value. Reading the Options Register will always return the clock ratemultiplier at which the board is operating.* 16750 UART only921.6 kbaud *14.7456 MHzX811460.8 kbaud *7.3728 MHzX401230.4 kbaud3.6864 MHzX210115.2 kbaud1.8432 MHzX1(default)00Maximum DataRateUART ClockFrequencyClock RateMultiplierRR0RR1Figure 12 --- Rate Register bit definitionAt powerup and reset, the Options Register is initialized to 0. The DSC-200/300will thus powerup in the x1 mode with software control of the clock rate multiplierenabled as long as the X2, X4, and X8 jumpers are not installed.Software can control high baud rates through a combination of changing theclock rate multiplier and the UART baud rate divisor. For example, a baud rate of230.4 kbps could be achieved by setting the clock rate multiplier to X2 mode (or byapplying the X2 jumper) and setting a software application for 115.2 kbps.Quatech DSC-200/300 User's Manual 17