zpuino_uart_rx.vhd

zpuino_uart_rx implements the receiver unit for uart

    zpuino_uart_rx
in std_logic clk
source clock
in

std_logic

rst
signal to reset
in std_logic rx
input data signal (data from the uart emitter)
in std_logic rxclk
input clock (clock from the uart emitter)
in std_logic read
signal to read data (the only effect is to reset data_av when data is not available, the data will be read normally even if read is not '1')
out std_logic [8] data
vector of the received data (complete only when data_av is '1')
out std_logic data_av
flag set when data is available (Note : read needs to be set to '1' otherwise data_av is not reset when data is not available)


How it works :
A baud is generated by a uart_brgen module, the frequency is 1/16 of clk.
The signal rx is oversampled and a majority vote zpuino_uart_mv_filter (with threshold : votes >= 10/16) is used, I assume this reduce the risk of error due to noise on the transmission.
The transmission begins when rx (oversampled) is set to '0' during a baud tick, then 8 bits are read from rx (oversampled) at each baud tick and stored in data.
After the 8 bits, if the rx (oversampled) is equals to '1' at the baud tick, the transmission is validated, data_av is set to '1'.

Date de dernière mise à jour : 13/06/2015

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