Datasheet

14-8 MCF5407 User’s Manual
Register Descriptions
14.3.3 Rx FIFO Threshold Register (RXLVL)
The Rx FIFO threshold register (RXLVL) supports UART1 only and is used in both UART
and modem modes. The threshold is one less than the value at which the Rx FIFO is
considered to be full for purposes of alerting the CPU that the Rx FIFO needs to be read.
Table 14-4 describes RXLVL fields.
3–0 SB Stop-bit length control. Selects the length of the stop bit appended to the transmitted character.
Stop-bit lengths of 9/16th to 2 bits are programmable for 6–8 bit characters. Lengths of 1 1/16th to 2
bits are programmable for 5-bit characters. In all cases, the receiver checks only for a high condition at
the center of the first stop-bit position, that is, one bit time after the last data bit or after the parity bit, if
parity is enabled. If an external 1x clock is used for the transmitter, clearing bit 3 selects one stop bit
and setting bit 3 selects 2 stop bits for transmission. Not used in modem mode.
SB 5 Bits 6–8 Bits SB 5 Bits 6–8 Bits SB 5–8 Bits SB 5–8 Bits
0000 1.063 0.563 0100 1.313 0.813 1000 1.563 1100 1.813
0001 1.125 0.625 0101 1.375 0.875 1001 1.625 1101 1.875
0010 1.188 0.688 0110 1.438 0.938 1010 1.688 1110 1.938
0011 1.250 0.750 0111 1.500 1.000 1011 1.750 1111 2.000
754 0
Field — RXLVL
Reset 000 0_0000
R/W R/W
Address MBAR + 0x201
Figure 14-4. Rx FIFO Threshold Register (RXLVL)
Table 14-4. RXLVL Field Descriptions
Bits Name Description
7–5 — Reserved, should be cleared.
4–0 RXLVL Rx FIFO full threshold level. Values of 0000–1111 specify 1–32 bytes. The Rx FIFO is full when the
number of bytes in the FIFO equals or exceeds the Rx threshold. Although FIFO thresholds are in
bytes, data is written into and read out of the FIFOs in numbers of samples, as follows:
• 1 sample = 1 byte for 8-bit CODEC and UART modes,
• 1 sample = 2 bytes for 16-bit CODEC and AC ‘97 modes
For choosing threshold values, AC ‘97 samples should be thought of as 2-byte entities.
The Rx threshold is RXLVL + 1, so RXLVL = [(# samples) * (# bytes per sample)] - 1. For example,
for Rx FIFO to indicate full when 13 or more samples have arrived, calculate RXLVL as follows:
• For 8-bit CODEC or UART mode, RXLVL = [(13 samples) * (1 byte per sample)] - 1 = 12 bytes
• For 16-bit CODEC or AC ‘97 modes, RXLVL = [(13 samples) * (2 bytes per sample)] - 1 = 25
bytes
Table 14-3. UMR2n Field Descriptions (Continued)
Bits Name Description