Renesas CPU Board M3A-HS19 Instrukcja Użytkownika Pobierz pdf (Strona 19)

SH7285/SH7286 USB Function Module

USB to Serial Conversion Application Note

2.5.2 Bulk IN Transfer

A bulk IN transfer consists of single or multiple transactions. The USB host sends an IN token in the IN transaction.

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. When the USB device receives the IN token although it is unable to send data packets, it returns a

NAK handshake to the USB host.

Figure 2.16 shows the IN Transaction flowchart.

When the USB function module receives an IN token although there is no valid data in the EP2FIFO, it automatically

returns a NAK handshake to the USB host. The USB function module determines if there is any valid data in the

EP2FIFO using the EP2PKTE bit in the USBTRG register. When the module receives the IN token when there is

valid data in the EP2FIFO, the USB function module sends the data in the EP2FIFO to the USB host and waits for an

ACK handshake from the USB host. When the ACK handshake is received, the USB function module sets the data

transmit complete flag using the EP2EMPTY bit in the USBIFR0 register.

The sample program periodically transfers data in bulk transfer mode within the main loop. When the serial

communication generates data in the bulk IN transfer RAM that should be transmitted to the USB host, the sample

program confirms if the EP2FIFO is empty. When the EP2FIFO is empty, the sample program writes the data in the

EP2FIFO, sets the PE2PKTE bit to 1, and enables the data in the EP2FIFO. When the EP2FIFO is not empty, the

sample program

is idle and waits for the USB function module to finish transferring data to the USB host.

Idle

IN token

ACK

Idle

Token

Data

Handshake

DATA0/1 NAK STALL

Packet issued by the host

Packet issued by the device

Figure 2.16 IN Transaction

REJ05B1152-0100/Rev.1.00 May 2008 Page 19 of 35

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