Renesas CPU Board M3A-HS19 Instrukcja Użytkownika Pobierz pdf (Strona 10)

SH7285/SH7286 USB Function Module

USB to Serial Conversion Application Note

2.4.2 Data Stage

The Data stage of the control IN transfer is composed of single or multiple data transactions. This is called “Data IN

stage processing”. The Data stage of the control OUT transfer is composed of

one data OUT transaction. This is

called “Data OUT stage processing”.

(1) Data IN Stage

First, the USB host sends an IN token. When the USB device receives the IN token, it sends

a data packet to the USB

host and waits for an ACK handshake from the USB host. If the USB device cannot send a data packet when it

receives the IN token, it returns a NAK handshake to the USB host.

Figure 2.7 shows the data IN transaction

flowchart.

When the USB function module receives an IN token without valid data in the

EP0iFIFO, it automatically returns a

NAK handshake to the USB host. When the module receives an IN token with valid data in the EP0iFIFO, it sends the

data in the EP0iFIFO to the USB host and waits for an ACK handshake from the USB host. When the USB function

module receives an ACK handshake, it generates the data transmit complete interrupt using the EP0iTS bit in the

USBIFR0 register. On the contrary, when the module receives an OUT token that indicates the Data IN stage has been

completed, it generates the data receive complete interrupt using the EP0oTS bit in the USBIFR0 register.

The sample program identifies the type of the interrupt while it is being processed. When it is the data receive

complete interrupt (the EP0oTS bit in the USBIFR0 register), the sample program advances to the Status stage. When

it is the data transmit complete interrupt (the EP0iTS bit in the USBIFR0 register), data that should be sent to the USB

host is written in the EP0iFIFO, and the sample program waits for the next interrupt.

Figure 2.8 shows an operation

flowchart of the Data IN stage by the sample program.

Idle

IN token

ACK

Idle

Token

Data

Handshake

DATA0/1 NAK STALL

Packet issued by the host

Packet issued by the device

Figure 2.7 Data IN Transaction

REJ05B1152-0100/Rev.1.00 May 2008 Page 10 of 35

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