6 fifo control register (fcr) – Intel MD566X User Manual

Page 124

56K V.92 Data, Fax, and Voice Chipset

124

Intel Confidential

Programmer’s Guide

10.1.6 FIFO Control Register (FCR)

This write-only register is used to enable the receiver and transmitter FIFOs, clear the FIFOs, set the RCVR FIFO trigger level, and
select the DMA signaling type.

Bit 2

Number of Stop Bits (STB) – This bit specifies the number of stop bits transmitted and received in each
serial character. When STB is set to “0”, one stop bit is generated for each transmitted data character. When
STB is set to “1” and the word length (WLS1 and WLS0) is equal to 6, 7, or 8 bits, then two stop bits are gen-
erated for each transmitted data character. When STB is set to “1” and the word length (WLS1 and WLS0) is
equal to 5 bits, then one and a half stop bits are generated for each transmitted data character. The receiver
only checks for the first stop bit, regardless of the number of stops bits transmitted.

Bits 1:0

Word Length Select Bits (WLS1 and WLS0) – These two bits specify the data character word length of
the transmitted and received data. The supported word lengths are provided below.

Bits 7:6

MSB and LSB (RCVR Trigger Bits)–FCR bits 7 and 6 are used to set the trigger level for the RCVR FIFO
interrupt.

Bits 5:3

Reserved–Bits 5, 4, and 3 are reserved for future enhancements.

Bit 2

XFIFOR (XMIT FIFO Reset)–When set to “1”, this bit clears all the bytes in the XMIT FIFO and resets the
internal counter logic to “0”. The internal shift register is not cleared by the XFIFOR bit. This bit is automati-
cally cleared by the modem.

Bit 1

RFIFOR (RCVR FIFO Reset)–When set to “1”, this bit clears all the bytes in the RCVR FIFO and resets the
internal counter logic to “0”. The internal shift register is not cleared by the RFIFOR bit. This bit is automati-
cally cleared by the modem.

Bit 0

FIFOE (FIFO Enable)–This bit when set to “1”, enables both the XMIT and RCVR FIFOs. This bit must be a
“1” whenever writing to any other FIFO bit. If FIFO is not set to “1”, then the DTE can not program any of the
FIFO functions.

Bit 1

Bit 0

Word Length

5 bits

6 bits

7 bits

8 bits

RCVR Trig. RCVR Trig. Reserved

Reserved

DMA

XFIFOR

RFIFOR

FIFOE

(write-only)

Bit 7

Bit 6

RCVR FIFO

Trigger Level (Bytes)