AT90SCR100 datasheet(163/433 Pages) ATMEL

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163

TPR0327AY–SMS–30Jan09

AT90SCR100

14.7

Double Buffering

This special feature available on the endpoints 1, 2 and 3 allows the user to save time during

USB transfers.

It is specially recommended for BULK data transfers but is also suitable for ISOCHRONOUS or

INTERRUPT. CONTROL is not possible on these double buffered endpoints.

The double buffering uses two different data banks of the endpoint size. Its management

remains transparent for the user. The advantages of the double buffering are the followings:

• When receiving data from the host, the software can process the data received in one of the

two banks while the second is being filled. The endpoints that do not have the double

buffering capability must wait for their DPRAM to be emptied by the software before being

ready to receive new data.

• When sending data to the host, the software can fill the free bank while the USB module is

sending data from the other one. The endpoints that do not have this feature must wait for the

previous data to be sent before being allowed to fill again the single bank.

The two following figures provide code algorithm for sending data to the host and receiving data

from the host (respectively IN and OUT tokens). They are also valid for endpoints operating nor-

mally (without the double buffering capability).

Figure 14-4.

Sending Data Packets (Single Buffering)

The figure is correct if several data packets have to be sent. If only one packet is to

be sent the testing of the bit USBCSE.TXPB must be ignored.

FILL DPRAM

SET bit USBCSEX.TXPB

USBCSEX.TXPB = 0 ?

YES

USBCSEX.TXC = 1 ?

(POLLING or INTERRUPT)

YES

CLEAR bit USBCSEX.TXC

LAST DATA PACKET REACHED ?

YES

END

USBCSEX.TXPB = 0 ?

YES

Note

AT90SCR100 Datasheet(PDF) 163 Page - ATMEL Corporation