W83877TF/W83877TG
Publication Release Date: May 2006
-59- Revision 0.7
7.3.13 ECP Operation
The host must negotiate on the parallel port to determine if the peripheral supports the ECP protocol
before ECP operation. After negotiation, it is necessary to initialize some of the port bits. The following
are required:
(a) Set direction = 0, enabling the drivers.
(b) Set strobe = 0, causing the nStrobe signal to default to the deasserted state.
(c) Set autoFd = 0, causing the nAutoFd signal to default to the deasserted state.
(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 operations 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 W83877TF/TG 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.
7.3.14 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.
