USBN9604-28MX/NOPB National Semiconductor, USBN9604-28MX/NOPB Datasheet - Page 26

• Manufacturer Part Number: USBN9604-28MX/NOPB
• Description: IC,Bus Controller,SOP,28PIN
• Manufacturer: National Semiconductor

Specifications of USBN9604-28MX/NOPB

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

6.0 Functional Description
(Continued)
A packet written to the FIFO is transmitted if an IN token for the respective endpoint is received. If an error condition is de-
tected, the packet data remains in the FIFO and transmission is retried with the next IN token.
The FIFO contents can be flushed to allow response to an OUT token or to write new data into the FIFO for the next IN token.
If an OUT token is received for the FIFO, the firmware is informed that the FIFO has received data only if there was no error
condition (CRC or STUFF error). Erroneous receptions are automatically discarded.
Transmit Endpoint FIFO Operation (TXFIFO1, TXFIFO2, TXFIFO3)
The Transmit FIFOs for Endpoints 1, 3 and 5 support bulk, interrupt and isochronous USB packet transfers larger than the
actual FIFO size. Therefore. the firmware must update the FIFO contents while the USB packet is transmitted on the bus.
Figure 21 illustrates the operation of the transmit FIFOs.
FLUSH (Resets TXRP and TXWP)
TXRP
TFxS - 1
0x0
+
TXFL = TXWP - TXRP
+
Tx FIFO X
TXWP
+
TCOUNT = TXRP - TXWP (= TFxS - TXFL)
Figure 21. Tx FIFO Operation
TFxS
Transmit FIFO x Size. This is the total number of bytes available within the FIFO.
TXRP
Transmit Read Pointer. This pointer is incremented every time the Endpoint Controller reads from the transmit FIFO. This
pointer wraps around to zero if TFxS is reached. TXRP is never incremented beyond the value of the write pointer TXWP.
An underrun condition occurs if TXRP equals TXWP and an attempt is made to transmit more bytes when the LAST bit in
the TXCMDx register is not set.
TXWP
Transmit Write Pointer. This pointer is incremented every time the firmware writes to the transmit FIFO. This pointer wraps
around to zero if TFxS is reached.
If an attempt is made to write more bytes to the FIFO than actual space available (FIFO overrun), the write to the FIFO is
ignored. If so, TCOUNT is checked for an indication of the number of empty bytes remaining.
TXFL
Transmit FIFO Level. This value indicates how many bytes are currently in the FIFO.
A FIFO warning is issued if TXFL decreases to a specific value. The respective WARNx bit in the FWR register is set if TXFL
is equal to or less than the number specified by the TFWL bit in the TXCx register.
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