W83877 Winbond Electronics Corp America, W83877 Datasheet - Page 66

• Manufacturer Part Number: W83877
• Description: Winbond I/O
• Manufacturer: Winbond Electronics Corp America

W83877F
(d) Set mode = 011 (ECP Mode)
ECP address/RLE bytes or data bytes may be sent automatically by writing the ecpAFifo or ecpDFifo,
respectively.
Mode Switching
Software will execute P1284 negotiation and all operation prior to a data transfer phase under
programmed I/O control (mode 000 or 001). 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 be changed only in mode 001.
When 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 waits for all the data to be read from the
FIFO before changing back to mode 000 or 001.
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.
Data Compression
The W83877F supports run length encoded (RLE) decompression in hardware and can transfer
compressed data to a peripheral. Note that the odd (RLE) compression in hardware is not supported.
In order to transfer data in ECP mode, the compression count is written to the ecpAFifo and the data
byte is written to the ecpDFifo.
5.3.14 FIFO Operation
The FIFO threshold is set in configuration register 5. All data transfers 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 by selecting the Parallel Port FIFO mode or ECP Parallel Port Mode. After a reset, the FIFO
is disabled.
5.3.15 DMA Transfers
DMA transfers are always to or from the ecpDFifo, tFifo, or CFifo. The DMA uses the standard PC
DMA services. The ECP requests DMA transfers from the host by activating the PDRQ pin. The DMA
will empty or fill 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.
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