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W83627UHG
Publication Release Date: March 24, 2008
-126-
Revision 1.44
11.3.12.1.
Mode Switching
The software must handle P1284 negotiation and all operations prior to a data transfer in SPP or PS/2
modes (000 or 001). The hardware provides an automatic control line handshake, moving data
between the FIFO and the ECP port, only in the data transfer phase (mode 011 or 010).
If the port is in mode 000 or 001, it may switch to any other mode. If the port is not in mode 000 or 001,
it can only be switched into mode 000 or 001. The direction can only be changed in mode 001.
In extended forward mode, the software should wait for the FIFO to be empty before switching back to
mode 000 or 001. In ECP reverse mode, the software should wait for all the data to be read from the
FIFO before changing back to mode 000 or 001.
11.3.12.2.
Command/Data
ECP mode allows the transfer of normal 8-bit data or 8-bit commands. In the forward direction, normal
data are transferred when HostAck is high, and an 8-bit command is transferred when HostAck is low.
The most significant bits of the command indicate whether it is a run-length count (for compression) or
a channel address.
In the reverse direction, normal data are transferred when PeriphAck is high, and an 8-bit command is
transferred when PeriphAck is low. The most significant bit of the command is always zero.
11.3.12.3.
Data Compression
The W83627UHG hardware supports RLE decompression and can transfer compressed data to a
peripheral. Odd (RLE) compression is not supported in the hardware, however. In order to transfer
data in ECP mode, the compression count is written to ecpAFifo and the data byte is written to
ecpDFifo.
11.3.12.4.
FIFO Operation
The FIFO threshold is set in CR5. All data transferred to or from the parallel port can proceed in DMA
or Programmed I/O (non-DMA) mode, as indicated by the selected mode. The FIFO is used in Parallel
Port FIFO mode or ECP Parallel Port Mode. After a reset, the FIFO is disabled.
11.3.13
DMA Transfers
DMA transfers are always to or from the ecpDFifo, tFifo, or CFifo. DMA uses the standard PC DMA
services. The ECP requests DMA transfers from the host by activating the PDRQ pin. The DMA
empties or fills the FIFO using the appropriate direction and mode. When the terminal count in the
DMA controller is reached, an interrupt is generated, and serviceIntr is asserted, which will disable the
DMA.
11.3.14
Programmed I/O (NON-DMA) Mode
The ECP and parallel port FIFOs can also be operated using interrupt-driven, programmed I/O.
Programmed I/O transfers are
1. To the ecpDFifo at 400H and ecpAFifo at 000H