LPC47N237-MD SMSC [SMSC Corporation], LPC47N237-MD Datasheet - Page 64

• Manufacturer Part Number: LPC47N237-MD
• Description: 3.3V I/O CONTROLLER FOR PORT REPLICATORS AND DOCKING STATIONS
• Manufacturer: SMSC [SMSC Corporation]

Note:
Note:
Revision 0.3 (10-26-04)
disabling DMA. In order to prevent possible blocking of refresh requests a DMA cycle shall not be
requested for more than 32 DMA cycles in a row. The FIFO is enabled directly by the host initiating a DMA
cycle for the requested channel, and addresses need not be valid. An interrupt is generated when a TC
cycle is received. (Note: The only way to properly terminate DMA transfers is with a TC cycle.)
DMA may be disabled in the middle of a transfer by first disabling the host DMA controller. Then setting
serviceIntr to 1, followed by setting dmaEn to 0, and waiting for the FIFO to become empty or full.
Restarting the DMA is accomplished by enabling DMA in the host, setting dmaEn to 1, followed by setting
serviceIntr to 0.
DMA Mode - Transfers from the FIFO to the Host
In the reverse mode, the peripheral may not continue to fill the FIFO if it runs out of data to transfer, even if
the chip continues to request more data from the peripheral.
The ECP requests a DMA cycle whenever there is data in the FIFO. The DMA controller responds to the
request by reading data from the FIFO. The ECP stop requesting DMA cycles when the FIFO becomes
empty or when a TC cycle is received, indicating that no more data is required. If the ECP stops requesting
DMA cycles due to the FIFO going empty, then a DMA cycle is requested again as soon as there is one
byte in the FIFO. If the ECP stops requesting DMA cycles due to the TC cycle, then a DMA cycle is
requested again when there is one byte in the FIFO, and serviceIntr has been re-enabled.
Programmed I/O Mode or Non-DMA Mode
The ECP or parallel port FIFOs may also be operated using interrupt driven programmed I/O. Software can
determine the writeIntrThreshold, readIntrThreshold, and FIFO depth by accessing the FIFO in Test Mode.
Programmed I/O transfers are to the ecpDFifo at 400H and ecpAFifo at 000H or from the ecpDFifo located
at 400H, or to/from the tFifo at 400H. To use the programmed I/O transfers, the host first sets up the
direction and state, sets dmaEn to 0 and serviceIntr to 0.
The ECP requests programmed I/O transfers from the host by activating the interrupt. The programmed
I/O will empty or fill the FIFO using the appropriate direction and mode.
A threshold of 16 is equivalent to a threshold of 15. These two cases are treated the same.
Programmed I/O - Transfers from the FIFO to the Host
In the reverse direction an interrupt occurs when serviceIntr is 0 and readIntrThreshold bytes are available
in the FIFO. If at this time the FIFO is full it can be emptied completely in a single burst, otherwise
readIntrThreshold bytes may be read from the FIFO in a single burst.
readIntrThreshold =(16-<threshold>) data bytes in FIFO
An interrupt is generated when serviceIntr is 0 and the number of bytes in the FIFO is greater than or equal
to (16-<threshold>). (If the threshold = 12, then the interrupt is set whenever there are 4-16 bytes in the
FIFO). The host must respond to the request by reading data from the FIFO. This process is repeated
until the last byte is transferred out of the FIFO. If at this time the FIFO is full, it can be completely emptied
in a single burst, otherwise a minimum of (16-<threshold>) bytes may be read from the FIFO in a single
burst.
DATASHEET
Page 64
3.3v I/O Controller for Port Replicators and Docking Stations
SMSC DS – LPC47N237