In transactions with no data packet, the device.
Not used in isochronous transactions.
Chapter 14
324
Control transfers always use DATA0 in the Setup stage, use DATA1 in the first
transaction of the Data stage, toggle the value in any additional Data-stage
transactions, and use DATA1 in the Status stage. Bulk and interrupt endpoints
toggle the value in every transaction, resetting the data toggle only after a bus
reset or on completing a Set Configuration, Set Interface, or Clear Feature(
ENDPOINT HALT) request.
325
15
"
%
Vendors who offer USB controllers designed specifically for use in virtual COM
ports are Future Technology Devices International (FTDI) (www.ftdichip.
com), Prolific Technology, Inc. (www.prolific.com.tw), and Silicon Laboratories
(www.silabs.com). The chips from these vendors function in similar ways.
These chips are sometimes called USB to UART bridges. This chapter describes
FTDI??™s chips and driver.
FTDI has several USB interface chips that manage enumeration and other bus
communications completely in hardware. The company provides free USB virtual
COM-port drivers for use with the chips. The chips don??™t require any
USB-specific firmware at all but can store device-specific descriptor values in
EEPROM if desired. A microcontroller or other CPU interfaces to the controller
via a serial or parallel interface.
Pages:
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338