Quatech QSC-200 User Manual page 17

A standard serial port operates at a clock speed of 1.8432 MHz. In order to achieve
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 the clock rate multiplier bits in the
Options Register.
Software can determine the UART clock frequency by reading the clock rate multiplier
bits RR1 and RR0 in the Options Register as shown in Figure 12. RR1 and RR0 can be set by
writing to the Options Register if the X2, X4, and X8 jumpers (J17-J19) are all removed. If one
of these jumpers 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 which the board is operating.
RR1 RR0
0
0
1
1
At powerup and reset, the Options Register is initialized to 0. The QSC-200/300 will
thus powerup in the x1 mode with software control of the clock rate multiplier enabled as long as
the X2, X4, and X8 jumpers are not installed.
Software can control high baud rates through a combination of changing the clock rate
multiplier and the UART baud rate divisor. For example, a baud rate of 230.4 kbps could be
achieved by setting the clock rate multiplier to X2 mode (or by applying the X2 jumper) and
setting a software application for 115.2 kbps.
Quatech QSC-200/300 Users Manual
Clock Rate
Multiplier
X1
0
(default)
1 X2
0 X4
1 X8
Figure 12 --- Rate Register bit definition
UART Clock
Frequency
1.8432 MHz
3.6864 MHz
7.3728 MHz
14.7456 MHz
Maximum Data
Rate
115.2 kbaud
230.4 kbaud
460.8 kbaud *
921.6 kbaud *
* 16750 UART only
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