UM10208_2
© NXP B.V. 2007. All rights reserved.
User manual
Rev. 02 — 1 June 2007
293 of 362
NXP Semiconductors
UM10208
Chapter 23: LPC2800 SD/MMC
4.3.11 Status flags
lists the data path status flags (see
Section 23–5.12 “Status Register
(MCIStatus - 0x8010 0034)” on page 300
for more information).
4.3.12 CRC generator
The CRC generator calculates the CRC checksum only for the data bits in a single block,
and is bypassed in data stream mode. The checksum is a 16 bit value:
CRC[15:0] = Remainder (M(x)
×
x15 ) / G(x)
G(x) = x16 + x12 + x5 + 1
M(x) - (first data bit)
×
xn + ... + (last data bit)
×
x0
4.3.13 Data FIFO
The data FIFO (first-in-first-out) subunit is a data buffer with transmit and receive logic.
The FIFO contains a 32 bit wide, 16-word deep data buffer, and transmit and receive
logic.
Depending on two signals from the data path subunit, TxActive and RxActive, the FIFO
can be disabled, transmit enabled, or receive enabled. TxActive and RxActive are
mutually exclusive:
•
The transmit FIFO refers to the transmit logic and data buffer when TxActive is
asserted (see Transmit FIFO)
•
The receive FIFO refers to the receive logic and data buffer when RxActive is
asserted (see Receive FIFO).
Table 328. Data path status flags
Flag
Description
TxFifoFull
Transmit FIFO is full.
TxFifoEmpty
Transmit FIFO is empty.
TxFifoHalfEmpty
Transmit FIFO is half full.
TxDataAvlbl
Transmit FIFO data available.
TxUnderrun
Transmit FIFO underrun error.
RxFifoFull
Receive FIFO is full.
RxFifoEmpty
Receive FIFO is empty.
RxFifoHalfFull
Receive FIFO is half full.
RxDataAvlbl
Receive FIFO data available.
RxOverrun
Receive FIFO overrun error.
DataBlockEnd
Data block sent/received.
StartBitErr
Start bit not detected on all data signals in wide bus mode.
DataCrcFail
Data packet CRC failed.
DataEnd
Data end (data counter is zero).
DataTimeOut
Data timeout.
TxActive
Data transmission in progress.
RxActive
Data reception in progress.