Telephone Signalling Transceiver / Least Cost Router
CMX860
of a Stop bit are then checked and the data bits in the Rx Data Buffer copied to the 'C-BUS' Rx Data
Register.
Figure 6a Rx Modem Data Paths
Whenever a new character is copied into the 'C-BUS' Rx Data Register, the Rx Data Ready flag bit of the
Status Register is set to 1 to prompt the µC to read the new data, and, in Start-stop mode, the Even Rx
Parity flag bit of the Status Register is updated.
In Start-stop mode, if the Stop bit is missing (received as a ‘0’ instead of a ‘1’) the received character will
still be placed into the Rx Data Register and the Rx Data Ready flag bit set, but the Status Register Rx
Framing Error bit will also be set to ‘1’ and the USART will re-synchronise onto the next ‘1’ – ‘0’ (Stop –
Start) transition. The Rx Framing Error bit will remain set until the next character has been received.
Figure 6b Rx USART Function (Start-stop mode, 8 Data Bits + Parity)
If the µC has not read the previous data from the Rx Data Register by the time that new data is copied to
it from the Rx Data Buffer then the Rx Data Overflow flag bit of the Status Register will be set to 1.
The Rx Data Ready flag and Rx Data Overflow bits are cleared to 0 when the Rx Data Register is read
by the µC.
ã 2002 Consumer Microcircuits Limited
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D/860/5
CMLMICRO [ CML MICROCIRCUITS ]
