Rainbow Electronics AT89C5132 - Manual (Page 8)

8
AT89C5132
4256A–USB–06/03
Physical Layer The USB norm specifies all the transfers over the USB line. The USB specification also
includes several CLASS and SUB-CLASS specifications. These stand-alone documents
are used by the manufacturer to implement a USB link between a PC and a device sup-
porting the In-System Programming. Mostly, the USB specification is implemented by
hardware (automatic reply, handshakes, timings, ...) and the USB Classes and Sub-
Classes are implemented by software at a data level.
Figure 3. USB Bus Topography
The USB used to transmit information has the following configuration:
•
USB DFU using the Default Control Endpoint only (endpoint 0) with a 32 bytes
length.
• 48 MHz for USB controller: frequency auto-detection performed by the bootloader.
48 MHz Frequency Auto-
generation The following table shows the allowed frequencies compatible with the USB bootloader
48 MHz auto-generation.
PC (Host)
application (Device)
USB line
Downstream Transfer: OUT
Upstream Transfer: IN
PC driver
PC application Device Driver/API
Firmware
12 MHz 16 MHz 20 MHz
X1 - X2 OK OK OK