GPS Receiver A1030-A
endpoints can be used. The USB_IP interfaces with the USB host and detects to-
ken packets, handles data transmission/reception, and processes handshake pack-
ets as required by the USB standard. Transaction formatting is performed by hard-
ware, including CRC generation and checking.
Each endpoint is associated with a buffer description block indicating where the
endpoint related memory area is located, how large it is or how many bytes must be
transmitted. When a token for a valid function/endpoint pair is recognized by the
USB_IP, the related data transfer (if required and if the endpoint is configured)
takes place, with the USB_IP buffering data loaded in an internal 16 bit long regis-
ter, and performing memory access to the dedicated buffer. When all data have
been transferred, if needed, the proper handshake packet over the USB is gener-
ated or expected, according to the direction of the transfer. At the end of the trans-
action, an endpoint specific interrupt is generated: reading status registers and/or
using different interrupt response routines, the microcontroller can determine which
endpoint has to be served, which type of transaction took place, if errors occurred
(bit stuffing, format, CRC, protocol, missing ACK, over/underrun, etc....). Special
support is offered to isochronous transfers and high throughput bulk transfers, im-
plementing a double buffer usage which allows having always an available buffer
for the USB_IP while the microcontroller uses the other one.
The unit can be placed in low-power mode (SUSPEND mode), by writing in a con-
trol register whenever required. At this time, all static power dissipation is avoided,
and the macrocell clock can be slowed down or stopped. The detection of activity at
the USB inputs while in low-power mode wakes the device up asynchronously. A
special interrupt source can be connected directly to a wake-up line so as to allow
the system to immediately restart normal clock generation and/or support direct
clock start/stop.
A1030A
: USBDN is available on pin 44 and USBDP on pin 42. The 48MHz USB
clock has to be provided on pin 14 (P1.10).
Page 32 of 37
User’s Manual
V2.0 - 07/05
