Renesas CPU Board M3A-HS19 Manual de usuario descargar pdf (Pagina 12)

SH7285/SH7286 USB Function Module

USB to Serial Conversion Application Note

(2) Data OUT Stage

The USB host sends an OUT token and a data packet. The USB device receives the OUT token first, then receives the

data packet, and then returns an ACK handshake. When the USB device cannot receive the data packet after it

receives the OUT token, it ignores subsequent data packets, and returns a NAK handshake. When the USB host

receives a NAK handshake, it tries to resend the OUT token and data packet.

Figure 2.9 shows the Data OUT

Transaction flowchart.

When the USB function module cannot receive data packets, when it receives the OUT token, it automatically

discards the subsequent data packet and returns a NAK handshake to the USB host. When it receives the OUT token

when it can accept data, it holds the data packet from the USB host in the EP0oFIFO and returns an ACK handshake

to the USB host. After the USB function module transmits an ACK handshake, it generates the data receive complete

interrupt using the EP0oTS bit in the USBIFR0 register. When the function module receives the IN token that

indicates the Data OUT stage is completed, it generates the IN token receive interrupt using the EP0iTR bit in the

USBIFR0 register.

The sample program identifies the type of the interrupt while it is being processed. When it is not 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 receive complete interrupt (the EP0oTS bit in the USBIFR0 register), the sample program reads data in

the EP0oFIFO, sets the EP0oFIFO read complete bit, and waits for the next interrupt to be generated.

Figure 2.10

shows an operation flowchart of Data OUT stage by the sample program.

Idle

OUT token

Idle

Token

Data

Handshake

ACK

NAK STALL

DATA0/1

NYET

Packet issued by the host

Packet issued by the device

Figure 2.9 Data OUT Transaction

REJ05B1152-0100/Rev.1.00 May 2008 Page 12 of 35

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Renesas CPU Board M3A-HS19 Manual de usuario Pagina 12