TL16C754B

QUAD UART WITH 64BYTE FIFO

SLLS397A − NOVEMBER 1999 − REVISED JUNE 2004

10

POST OFFICE BOX 655303

functional description (continued)

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

Bit 6−0 cleared. Bit 7 reflects the inverse of

the CLKSEL pin value.

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

Bit 6 − 0 is cleared. Bit 7 reflects the inverse

of the CLKSEL pin value.

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 some signals 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 TL16C754B UART 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 interrupt identification register(IIR) indicates that an interrupt is pending and provides

the type of interrupt through IIR[5−0]. Table 4 summarizes the interrupt control functions.