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GR716-DS-UM, May 2019, Version 1.29
488
www.cobham.com/gaisler
GR716
Block transfers can be performed be setting the length field to n-1, where n denotes the number of
transferred words. For write accesses, the control byte and address is sent once, followed by the num-
ber of data words to be written. The address is automatically incremented after each data word. For
read accesses, the control byte and address is sent once and the corresponding number of data words is
returned.
48.2.2 Baud rate generation
The UART contains a 18-bit down-counting scaler to generate the desired baud-rate. The scaler is
clocked by the system clock and generates a UART tick each time it underflows. The scaler is
reloaded with the value of the UART scaler reload register after each underflow. The resulting UART
tick frequency should be 8 times the desired baud-rate.
If not programmed by software, the baud rate will be automatically discovered. This is done by
searching for the shortest period between two falling edges of the received data (corresponding to two
bit periods). When three identical two-bit periods has been found, the corresponding scaler reload
value is latched into the reload register, and the BL bit is set in the UART control register. If the BL bit
is reset by software, the baud rate discovery process is restarted. The baud-rate discovery is also
restarted when a ‘break’ or framing error is detected by the receiver, allowing to change to baudrate
from the external transmitter. For proper baudrate detection, the value 0x55 should be transmitted to
the receiver after reset or after sending break.
The best scaler value for manually programming the baudrate can be calculated as follows:
scaler = (((system_clk*10)/(baudrate*8))-5)/10
48.3
Registers
The core is programmed through registers mapped into APB address space.
Table 656.
AHB UART registers
APB address offset
Register
0x4
AHB UART status register
0x8
AHB UART control register
0xC
AHB UART scaler register