xr16m698 Exar Corporation, xr16m698 Datasheet - Page 13

• Manufacturer Part Number: xr16m698
• Description: 1.62v To 3.63v High Performance Octal Uart With 32-byte Fifo
• Manufacturer: Exar Corporation

REV. 1.0.0
The host may fill the transmit FIFO with up to 32 bytes of transmit data. The THR empty flag (LSR bit-5) is set
whenever the FIFO is empty. The THR empty flag can generate a transmit empty interrupt (ISR bit-1) when the
amount of data in the FIFO falls below its programmed trigger level. The transmit empty interrupt is enabled by
IER bit-1. The TSR flag (LSR bit-6) is set when TSR/FIFO becomes empty.
The receiver section contains an 8-bit Receive Shift Register (RSR) and 32 bytes of FIFO which includes a
byte-wide Receive Holding Register (RHR). The RSR uses the 16X (or the 8X or the 4X) clock for timing. It
verifies and validates every bit on the incoming character in the middle of each data bit. On the falling edge of
a start or false start bit, an internal receiver counter starts counting the number of 16X (or 8X or 4X) clocks.
After 8 (or 4 or 2) clocks the start bit period should be at the center of the start bit. At this time the start bit is
sampled and if it is still a logic 0 it is validated. Evaluating the start bit in this manner prevents the receiver from
assembling a false character. The rest of the data bits and stop bits are sampled and validated in this same
manner to prevent false framing. If there were any error(s), they are reported in the LSR register bits 2-4. Upon
unloading the receive data byte from RHR, the receive FIFO pointer is bumped and the error tags are
immediately updated to reflect the status of the data byte in RHR register. RHR can generate a receive data
ready interrupt upon receiving a character or delay until it reaches the FIFO trigger level. Furthermore, data
delivery to the host is guaranteed by a receive data ready time-out interrupt when data is not received for 4
word lengths as defined by LCR[1:0] plus 12 bits time. This is equivalent to 3.7-4.6 character times. The RHR
interrupt is enabled by IER bit-0.
The Receive Holding Register is an 8-bit register that holds a receive data byte from the Receive Shift
Register. It provides the receive data interface to the host processor. The RHR register is part of the receive
FIFO of 32 bytes by 11-bits wide, the 3 extra bits are for the 3 error tags to be reported in LSR register. When
the FIFO is enabled by FCR bit-0, the RHR contains the first data character received by the FIFO. After the
RHR is read, the next character byte is loaded into the RHR and the errors associated with the current data
byte are immediately updated in the LSR bits 2-4.
F
2.8
2.7.3
2.8.1
IGURE
6. T
Receiver
Transmitter Operation in FIFO Mode
Receive Holding Register (RHR) - Read-Only
RANSMITTER
16X or 8X or 4X Clock
Auto CTS Flow Control (CTS# pin)
(Xoff1/2 and Xon1/2 Reg.)
Flow Control Characters
Auto Software Flow Control
O
PERATION IN
1.62V TO 3.63V HIGH PERFORMANCE OCTAL UART WITH 32-BYTE FIFO
Data Byte
Transmit
FIFO
AND
Transmit Data Shift Register
F
LOW
Transmit
(TSR)
13
FIFO
C
ONTROL
M
ODE
THR Interrupt (ISR bit-1) falls
below the programmed Trigger
Level and then when becomes
empty. FIFO is Enabled by FCR
bit-0=1
XR16M698