XR16V654_0709 Datasheet, PDF (20/58 Pages) Exar Corporation – 2.25V TO 3.6V QUAD UART WITH 64-BYTE FIFO

XR16V654/654D
2.25V TO 3.6V QUAD UART WITH 64-BYTE FIFO
FIGURE 11. RECEIVER OPERATION IN FIFO AND AUTO RTS FLOW CONTROL MODE
REV. 1.0.2
16X or 8X or 4X Clock
( DLD[5:4] )
64 bytes by 11-bit wide
FIFO
Receive Data
Byte and Errors
Receive Data Shift
Register (RSR)
R e c e iv e
Data FIFO
R e c e iv e
Data
Data Bit
V a lid a tio n
Receive Data Characters
E x a m p le
: - RX FIFO trigger level selected at 16 bytes
(See Note Below)
Data falls to
8
RTS# re-asserts when data falls below the flow
control trigger level to restart remote transmitter.
Enable by EFR bit-6=1, M CR bit-1.
FIFO
Trigger=16
RHR Interrupt (ISR bit-2) programm ed for
desired FIFO trigger level.
FIFO is Enabled by FCR bit-0=1
Data fills to
56
RTS# de-asserts when data fills above the flow
control trigger level to suspend remote transmitter.
Enable by EFR bit-6=1, MCR bit-1.
RXFIFO 1
2.11 Auto RTS (Hardware) Flow Control
Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS#
output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control
features is enabled to fit specific application requirement (see Figure 12):
• Enable auto RTS flow control using EFR bit-6.
• The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled).
If using the Auto RTS interrupt:
Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the RTS#
pin makes a transition from low to high: ISR bit-5 will be set to logic 1.
2.12 Auto RTS Hysteresis
The V654 has a new feature that provides flow control trigger hysteresis while maintaining compatibility with
the XR16C850, ST16C650A and ST16C550 family of UARTs. With the Auto RTS function enabled, an interrupt
is generated when the receive FIFO reaches the selected RX trigger level. The RTS# pin will not be forced
HIGH (RTS off) until the receive FIFO reaches one trigger level above the selected trigger level in the trigger
table (Table 12). The RTS# pin will return LOW after the RX FIFO is unloaded to one level below the selected
trigger level. Under the above described conditions, the V654 will continue to accept data until the receive
FIFO gets full. The Auto RTS function is initiated when the RTS# output pin is asserted LOW (RTS On).
TABLE 7: AUTO RTS (HARDWARE) FLOW CONTROL
RX TRIGGER LEVEL
INT PIN ACTIVATION
RTS# DE-ASSERTED (HIGH)
(CHARACTERS IN RX FIFO)
RTS# ASSERTED (LOW)
(CHARACTERS IN RX FIFO)
8
8
16
0
16
16
56
8
56
56
60
16
60
60
60
56
20