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SAB 82532/SAF 82532
Asynchronous Serial Mode
Semiconductor Group
75
07.96
6.4.4
In ASYNC modes an optional in-band flow control is provided with the XON/XOFF
characters.
If MODE:FLON bit = ‘1’ then the transmitter output is controlled based on recognition of
the XON/XOFF characters at the receiver.
A new optional function ‘Disable XON/XOFF Storage’ bit (DXS) in the RFC register is
used to determine if the received in-band flow control characters (XON/XOFF) are to be
stored in the RFIFO or to be removed from the incoming data stream.
Setting the
control bit RFC:DXS = ‘1’ (in conjunction with MODE:FLON = ‘1’) causes the
XON/XOFF received characters to be discarded.
Normally with RFC/DXS = ‘0’ (and
on RESET condition) the received XON/XOFF characters are stored in the RFIFO along
with the data.
In-band Flow Control Transparency
6.4.5
If data transfer from system memory to the ESCC2 is done by DMA (DMA bit in XBCH
set), the number of characters to be transmitted is usually defined via the Transmit Byte
Count registers (XBCH, XBCL: bits XBC11 … XBC0).
However, if the ‘Transmit Continuously’ (XC) bit in XBCH is set, the byte count value is
ignored and the DMA interface of ESCC2 will continuously request for transmit data any
time 32 new characters can be stored in XFIFO.
Note: If the XC bit is reset during continuous transmission, the transmit byte count
becomes valid again, and the ESCC2 will request the amount of DMA transfers
programmed via XBC11 … XBC0. Otherwise, the continuous transmission is
stopped when a data underrun condition occurs in XFIFO, i.e. the DMA controller
does not transfer further data to ESCC2. In this case continuous ‘1’s (IDLE) are
transmitted.
Continuous Transmission (DMA mode only)