Endpoint Operation; Address Detection; Transmit And Receive Endpoint Fifos - NS USBN9603 Manual

6.0 Functional Description

6.2 ENDPOINT OPERATION

6.2.1

Address Detection

Packets are broadcast from the host controller to all the nodes on the USB network. Address detection is implemented in
hardware to allow selective reception of packets and to permit optimal use of microcontroller bandwidth. One function ad-
dress with seven different endpoint combinations is decoded in parallel. If a match is found, then that particular packet is
received into the FIFO; otherwise it is ignored.
The incoming USB Packet Address field and Endpoint field are extracted from the incoming bitstream. Then the address
field is compared to the Function Address register (FADR). If a match is detected, the Endpoint field is compared to all of
the Endpoint Control registers (EPCx) in parallel. A match then causes the payload data to be received or transmitted using
the respective endpoint FIFO.
6.2.2

Transmit and Receive Endpoint FIFOs

The device uses a total of seven transmit and receive FIFOs: one bidirectional transmit and receive FIFO for the mandatory
control endpoint, three transmit FIFOs and three receive FIFOs. As shown in Table 4, the bidirectional FIFO for the control
endpoint is 8 bytes deep. The additional unidirectional FIFOs are 64 bytes each for both transmit and receive. Each FIFO
can be programmed for one exclusive USB endpoint, used together with one globally decoded USB function address. The
firmware must not enable both transmit and receive FIFOs for endpoint zero at any given time.
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ADDR Field
FADR Register
match
Figure 19. USB Function Address/Endpoint Decoding
Endpoint Field
match
EPC0 Register
EPC1 Register
EPC2 Register
EPC3 Register
EPC4 Register
EPC5 Register
EPC6 Register
24
- USB Packet -
Receive/Transmit FIFO0
Transmit FIFO1
Receive FIFO1
Transmit FIFO2
Receive FIFO2
Transmit FIFO3
Receive FIFO3