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4.5.2 Clock Rate Multiplier
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, four, or 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 and X4
jumpers (J4-J5) 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.
921.6 kbaud14.7456 MHzX811
460.8 kbaud 7.3728 MHzX401
230.4 kbaud3.6864 MHzX210
115.2 kbaud1.8432 MHz
X1
(default)
00
Maximum Data
Rate
UART Clock
Frequency
Clock Rate
Multiplier
RR0RR1
Figure 12 --- Rate Register bit definition
At powerup and reset, the Options Register is initialized to 0. The
DSCLP-200/300 will thus powerup in the x1 mode with software control of the
clock rate multiplier enabled as long as the X2 or X4 or 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.
DSCLP/SSCLP-200/300 User's Manual 20