1.13.3 EZ-USB Interrupt Endpoints
Interrupt endpoints are almost identical to bulk endpoints. Fourteen EZ-USB endpoints
(EP1-EP7, IN, and OUT) may be used as interrupt endpoints. Interrupt endpoints have
maximum packet sizes up to 64, and contain a “polling interval” byte in their descriptor to
tell the host how often to service them. The 8051 transfers data over interrupt endpoints in
exactly the same way as for bulk endpoints. Interrupt endpoints are described in Chapter
6, "EZ-USB Bulk Transfers."
1.13.4 EZ-USB Isochronous Endpoints
Isochronous endpoints deliver high bandwidth, time critical data over USB. Isochronous
endpoints are used to stream data to devices such as audio DACs, and from devices such
as cameras and scanners. Time of delivery is the most critical requirement, and isochro-
nous endpoints are tailored to this requirement. Once a device has been granted an isoch-
ronous bandwidth slot by the host, it is guaranteed to be able to send or receive its data
every frame.
EZ-USB contains 16 isochronous endpoints, numbered 8-15 (8IN-15IN, and 8OUT-
15OUT). 1,024 bytes of FIFO memory are available to the 16 endpoints, and may be
FIFO memory to provide double-buffering. Using double buffering, the 8051 reads OUT
data from isochronous endpoint FIFOs containing data from the previous frame while the
host writes current frame data into the other buffer. Similarly, the 8051 loads IN data into
isochronous endpoint FIFOs that will be transmitted over USB during the next frame
while the host reads current frame data from the other buffer. At every SOF the USB
FIFOs and 8051 FIFOs switch, or ping-pong.
Isochronous transfers are described in Chapter 8, "EZ-USB Isochronous Transfers."
1.14 Fast Transfer Modes
The following versions of the EZ-USB have a fast transfer mode: AN2125SC,
AN2126SC, AN2135SC, AN2136SC, and AN2131QC, that is, those versions that have a
data bus (see Table 1-2). The fast transfer mode minimizes the transfer time from EZ-USB
core also supplies external FIFO read and write strobes to synchronize the transfers.
Using the fast transfer mode, the 8051 transfers a byte of data between an internal FIFO
and the external bus using a single 8051 MOVX instruction, which takes two cycles or
333 ns. Both Isochronous and Bulk endpoints can use this fast transfer mode.
Page 1-14
Chapter 1. Introducing EZ-USB
EZ-USB TRM v1.9
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