Quatech Asynchronous Communications Adapter QSCLP-100 - Manual (Page 4)

These jumpers force an increase of the UART input clock frequency by a factor
of two, four, or eight. This feature can allow legacy software to use baud rates above
115,200 bits per second. It is also useful if the serial port device driver does not
directly support setting the higher baud rates through the Options Register (see page 0).
If one of these jumpers is applied, it overrides any value written to the Options
Register to set the clock multiplier by software. The effective baud rate will be either
two, four, or eight times the value for which the UART itself is programmed.
The factory default is none of these jumpers applied, which allows for software
control of the clock multiplier via the Options Register. The Options Register powerup
default is for a standard times-1 clock of 1.8432 MHz for compatibility with standard
serial ports.
Figure 4 --- Clock multiplier jumper options
SPAD
X2
X4
X8
J2
J3
J4
J5
Force times-eight clock
Baud rates up to 921.6 kbps
SPAD
X2
X4
X8
J2
J3
J4
J5
Force times-two clock
Baud rates up to 230.4 kbps
SPAD
X2
X4
X8
J2
J3
J4
J5
Factory default
software control
SPAD
X2
X4
X8
J2
J3
J4
J5
Force times-four clock
Baud rates up to 460.8 kbps
QSCLP-100 User's Manual 3