TL16C752B-EP

3.3-V DUAL UART WITH 64-BYTE FIFO

SGLS153 – FEBRUARY 2003

9

POST OFFICE BOX 655303

functional description (continued)

software flow control example

Assumptions: UART1 is transmitting a large text file to UART2. Both UARTs are using software flow control with

single character Xoff (0F) and Xon (0D) tokens. Both have Xoff threshold (TCR [3:0]=F) set to 60 and Xon

threshold (TCR[7:4]=8) set to 32. Both have the interrupt receive threshold (TLR[7:4]=D) set to 52.

UART1 begins transmission and sends 52 characters, at which point UART2 generates an interrupt to its

processor to service the RCV FIFO, but assume the interrupt latency is fairly long. UART1 continues sending

characters until a total of 60 characters have been sent. At this time UART2 transmits a 0F to UART1, informing

UART2 is serviced and the processor reads enough data out of the RCV FIFO that the level drops to 32. UART2

now sends a 0D to UART1, informing UART1 to resume transmission.

reset

Table 2 summarizes the state of registers after reset.

Table 2. Register Reset Functions

REGISTER

RESET

CONTROL

RESET STATE

Interrupt enable register

RESET

All bits cleared

Interrupt identification register

RESET

Bit 0 is set. All other bits cleared.

FIFO control register

RESET

All bits cleared

Line control register

RESET

Reset to 00011101 (1D hex).

Modem control register

RESET

All bits cleared

Line status register

RESET

Bits 5 and 6 set. All other bits cleared.

Modem status register

RESET

Bits 0 – 3 cleared. Bits 4 – 7 input signals.

Enhanced feature register

RESET

All bits cleared

Receiver holding register

RESET

Pointer logic cleared

Transmitter holding register

RESET

Pointer logic cleared

Transmission control register

RESET

All bits cleared

Trigger level register

RESET

All bits cleared

NOTE: Registers DLL, DLH, SPR, Xon1, Xon2, Xoff1, Xoff2 are not reset by the top-level reset signal

RESET, i.e., they hold their initialization values during reset.

Table 3 summarizes the state of registers after reset.

Table 3. Signal Reset Functions

SIGNAL

RESET

CONTROL

RESET STATE

TX

RESET

High

RTS

RESET

High

DTR

RESET

High

RXRDY

RESET

High

TXRDY

RESET

Low

interrupts

The TL16C752B-EP has interrupt generation and prioritization (6 prioritized levels of interrupts) capability. The

interrupt enable register (IER) enables each of the 6 types of interrupts and the INT signal in response to an

interrupt generation. The IER can also disable the interrupt system by clearing bits 0–3, 5–7. When an interrupt

is generated, the IIR indicates that an interrupt is pending and provides the type of interrupt through IIR[5–0].

Table 4 summarizes the interrupt control functions.