Rainbow Electronics MAX3107 - Manual (Page 21)

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MAX3107
SPI/I
2
C UART with 128-Word FIFOs
and Internal Oscillator
RESUME are programmed in FlowLvl. With differing
HALT and RESUME levels, hysteresis can be defined for
the RTS/CLKOUT transitions.
When the RxFIFO fill level reaches the HALT level
(FlowLvl[3:0]), the MAX3107 deasserts RTS/CLKOUT.
RTS/CLKOUT remains deasserted until the RxFIFO is
emptied and the number of words falls to the RESUME
level.
Interrupts are not generated when the HALT and
RESUME levels are reached. This allows the host control-
ler to be completely disengaged from RTS flow control
management.
AutoCTS Control
When AutoCTS flow control is enabled, the UART auto-
matically starts transmitting data when the CTS input is
logic-level low and stops transmitting when CTS is logic-
high. This frees the host processor from managing this
timing-critical flow-control task. AutoCTS flow control is
enabled through FlowCtrl[1]: AutoCTS. During AutoCTS
flow control the CTS interrupt works normally. Set the
IRQEn[7]: CTSIntEn to 0 to disable CTS interrupts; then
ISR[7]: CTSInt is fixed to logic 0 and the host does not
receive interrupts from CTS. If CTS is set high during
transmission, the MAX3107 completes transmission of
the current word and halts transmission afterwards.
Turn the transmitter off by setting MODE1[1] to 1 before
enabling AutoCTS control.
Automatic Software (XON/XOFF)
Flow Control
When automatic software flow control is enabled, the
MAX3107 recognizes and/or sends predefined XON/
XOFF characters to control the flow of data across the
asynchronous serial link. Automatic flow works autono-
mously and does not involve host intervention, similar to
automatic hardware flow control. To reduce the chance
of receiving corrupted data that equals a single-byte
XON or XOFF character, the MAX3107 allows for double-
wide (16-bit) XON/XOFF characters. XON and XOFF are
programmed into the XON1, XON2 and XOFF1, XOFF2
registers.
FlowCtrl[7:3] are used for enabling and configuring auto
software flow control. An ISR[1] interrupt is generated
when XON or XOFF are received and details are found in
SpclCharInt. The IRQ can be masked by setting IRQEn[1]:
SpclChrIEn to 0.
Software flow control consists of transmitter control and
receiver overflow control, which can operate indepen-
dently of each other.
Figure 12. Echo Suppression Timing
TX
RX
DI TO RO PROPAGATION DELAY
HOLD DELAY STOP
BIT
RTS/CLKOUT