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4.4.2 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 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 (J10-J12)
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.
* 16750 UART only
921.6 kbaud *14.7456 MHzX811
460.8 kbaud *
7.3728 MHz
X4
0
1
230.4 kbaud3.6864 MHzX210
115.2 kbaud1.8432 MHz
X1
(default)
00
M
aximum 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 DSC-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 DSC
-200/300 User
'
s Manual
17