Quatech QSC(LP)-100 user manual Force High-Speed Uart Clock X2, X4, or X8, J3-J5

2.3 Force High-Speed UART Clock (X2, X4, or X8, J3-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 section 4.4).

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.

J2	SPAD	J2	SPAD
J3	X8	J3	X8
J4	X4	J4	X4
J5	X2	J5	X2
Factory default		Force times-two clock
software control		Baud rates up to 230.4 kbps
J2	SPAD	J2	SPAD
J3	X8	J3	X8
J4	X4	J4	X4
J5	X2	J5	X2
Force times-four clock		Force times-eight clock
Baud rates up to 460.8 kbps		Baud rates up to 921.6 kbps

Figure 4 --- Clock multiplier jumper options

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