MAX14830 Datasheet, PDF (26/68 Pages) Maxim Integrated Products – Quad Serial UART with 128-Word FIFOs

MAX14830
Quad Serial UART with 128-Word FIFOs
Echo suppression can operate simultaneously with auto
transceiver direction control (Figure 15).
Auto Hardware Flow Control
The MAX14830 is capable of automatic hardware (RTS
and CTS) flow control without the need for host proces-
sor intervention. When AutoRTS control is enabled,
the MAX14830 automatically controls the RTS hand-
shake without the need for host processor intervention.
AutoCTS flow control separately turns the MAX14830’s
transmitter on and off based on the CTS_ input. AutoRTS
and AutoCTS flow control are independently enabled
through FlowCtrl[1:0].
AutoRTS Control
AutoRTS flow control ensures that the Receive FIFO does
not overflow by signaling to the far end UART to stop
data transmission. The MAX14830 does this automatical-
ly by controlling RTS_. AutoRTS flow control is enabled
through FlowCtrl[0]: AutoRTS. The HALT and RESUME
levels determine the threshold levels at which RTS_ is
asserted and deasserted. HALT and RESUME are pro-
grammed in FlowLvl. With differing HALT and RESUME
levels, hysteresis can be defined for the RTS_ transitions.
When the RxFIFO fill level reaches the HALT level
(FlowLvl[3:0]), the MAX14830 deasserts RTS_. RTS_
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.
Tx FIFO
TRAN_LOS^TGM^XICITTER ^{TX_ DI} D
B
MAX14830
ECHO
RTS_ DE
SUPPRESSION
MAX14840E
A
RE
Rx FIFO
RECEIVER
RX_ RO
R
Figure 15. Half-Duplex with Echo Suppression
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 manag-
ing 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 dur-
ing transmission the MAX14830 completes transmission
of the current word and halts transmission afterwards.
Turn the transmitter off by setting MODE1[1] to 1 before
enabling AutoCTS control.
FIFO Interrupt Triggering
Receive and Transmit FIFO fill-dependent interrupts are
generated if FIFO trigger levels are defined. When the
number of words in the FIFOs reach or exceed a trigger
level, as programmed in FIFOTrgLvl, an ISR[3] or ISR[4]
interrupt is generated. There is no relationship between
the trigger levels and the HALT or RESUME levels.
The FIFO trigger level can, for example, be used for a
block data transfer, since it gives the host an indication
when a given block size of data is available for reading in
the Receive FIFO or available for transfer to the Transmit
FIFO.
Auto Software (XON/XOFF) Flow Control
When auto software flow control is enabled, the
MAX14830 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 auto hardware flow control. To reduce the chance of
receiving corrupted data that equals a single-byte XON
or XOFF character, the MAX14830 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 one another.
26  
Maxim Integrated