Quatech RS-422 Force High-Speed Uart Clock X2 or X4, J4-J5, Enable scratchpad registers

J2

J4

J5

SPAD

X4

X2

Figure 4 --- Enable scratchpad registers

2.4.2 Force High-Speed UART Clock (X2 or X4, J4-J5)

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 10).

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 or four 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 5 --- Clock multiplier jumper options

J2

J4

J5

SPAD

X4

X2

factory default

6 DSCLP/SSCLP-200/300 User's Manual