mcf5407 Freescale Semiconductor, Inc, mcf5407 Datasheet - Page 350

• Manufacturer Part Number: mcf5407
• Description: Mcf5407 Coldfire Integrated Microprocessor User
• Manufacturer: Freescale Semiconductor, Inc

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.
Bits
3–0
14-8
Bits
7–5
4–0
Address
Reset
Field
R/W
Name
RXLVL
SB
Name
—
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.
7
Reserved, should be cleared.
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:
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:
0000 1.063
0001 1.125
0010 1.188
0011 1.250
• 1 sample = 1 byte for 8-bit CODEC and UART modes,
• 1 sample = 2 bytes for 16-bit CODEC and AC ‘97 modes
• 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
SB
bytes
Table 14-3. UMR2n Field Descriptions (Continued)
Figure 14-4. Rx FIFO Threshold Register (RXLVL)
5 Bits
000
—
Table 14-4. RXLVL Field Descriptions
6–8 Bits
0.563
0.625
0.688
0.750
5
MCF5407 User’s Manual
0100
0101
0110
0111
SB
5 Bits
1.313
1.375
1.438
1.500
MBAR + 0x201
4
Description
Description
R/W
6–8 Bits
0.813
0.875
0.938
1.000
1000
1001
1010
1011
SB
0_0000
RXLVL
5–8 Bits
1.563
1.625
1.688
1.750
1100
1101
1110
1111
SB
5–8 Bits
1.813
1.875
1.938
2.000
0