
EM358x
100
Rev. 0.4
Figure 8-5. RTS/CTS Flow Control Connections
The UART RTS/CTS flow control options are selected by the SC_UARTFLOW and SC_UARTAUTO bits in the
SC1_UARTCFG register (see Table 8-12). Whenever the SC_UARTFLOW bit is set, the UART will not start
transmitting a character unless nCTS is low (asserted). If nCTS transitions to the high state (deasserts) while a
character is being transmitted, transmission of that character continues until it is complete.
If the SC_UARTAUTO bit is set, nRTS is controlled automatically by hardware: nRTS is put into the low state
(asserted) when the receive FIFO has room for at least two characters, otherwise is it in the high state
(unasserted). If SC_UARTAUTO is clear, software controls the nRTS output by setting or clearing the
SC_UARTRTS bit in the SC1_UARTCFG register. Software control of nRTS is useful if the external serial device
cannot stop transmitting characters promptly when nRTS is set to the high state (deasserted).
Table 8-12. UART RTS/CTS Flow Control Configurations
SC1_UARTCFG
Pins Used
Operating Mode
SC_UARTxxx
1
FLOW AUTO RTS
0
-
-
TXD, RXD No RTS/CTS flow control
1
0
0/1
TXD, RXD,
nCTS, nRTS
Flow control using RTS/CTS with software control of nRTS:
nRTS controlled by SC_UARTRTS bit in SC1_UARTCFG register
1
1
-
TXD, RXD,
nCTS, nRTS
Flow control using RTS/CTS with hardware control of nRTS:
nRTS is asserted if room for at least 2 characters in receive FIFO
1
The notation xxx means that the corresponding column header below is inserted to form the field name.
8.6.5
DMA
The DMA Channels section describes how to configure and use the serial receive and transmit DMA channels.
The receive DMA channel has special provisions to record UART receive errors. When the DMA channel
transfers a character from the receive FIFO to a buffer in memory, it checks the stored parity and frame error
status flags. When an error is flagged, the SC1_RXERRA/B register is updated, marking the offset to the first
received character with a parity or frame error. Similarly if a receive overrun error occurs, the SC1_RXERRA/B
registers mark the error offset. The receive FIFO hardware generates the INT_SCRXOVF interrupt and DMA
status register indicates the error immediately, but in this case the error offset is 4 characters ahead of the actual
overflow at the input to the receive FIFO. Two conditions will clear the error indication: setting the appropriate
SC_RXDMARST bit in the SC1_DMACTRL register, or loading the appropriate DMA buffer after it has unloaded.
8.6.6
Interrupts
UART interrupts are generated on the following events:
Transmit FIFO empty and last character shifted out (depending on SCx_INTMODE, either the 0 to 1 transition
or the high level of SC_UARTTXIDLE)
Transmit FIFO changed from full to not full (depending on SCx_INTMODE, either the 0 to 1 transition or the
high level of SC_UARTTXFREE)
Содержание EMBER EM358 series
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