ST16C1550 Просмотр технического описания (PDF) - Exar Corporation

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ST16C1550

2.97V TO 5.5V UART WITH 16-BYTE FIFO

Exar Corporation 

áç

REV. 4.2.0

ST16C1550/51

2.97V TO 5.5V UART WITH 16-BYTE FIFO

FIGURE 5. TRANSMITTER OPERATION IN NON-FIFO MODE

Data

Byte

Transmit

Holding

Register

(THR)

THR Interrupt (ISR bit-1)

Enabled by IER bit-1

16X Clock

Transmit Shift Register (TSR)

M

L

S

S

B

B

TXNOFIFO1

2.5.3 Transmitter Operation in FIFO Mode

The host may fill the transmit FIFO with up to 16 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.

2.6 Receiver

The receiver section contains an 8-bit Receive Shift Register (RSR) and 16 bytes of FIFO which includes a

byte-wide Receive Holding Register (RHR). The RSR uses the 16X 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 at the 16X clock rate. After 8 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.

2.6.1 Receive Holding Register (RHR) - Read-Only

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 16 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.

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