PIC16C745SLASHP datasheet(73/158 Pages) MICROCHIP

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Advanced Information

DS41124A-page 73

PIC16C745/765

SET_CONFIGURATION command. Once the device

is configured, the application can communicate with

the host using the GetUSB and PutUSB calls.

The USB peripheral detects several different errors

and handles most internally. The USB_ERR interrupt

notifies the microcontroller that an error has occurred.

No action is required by the device when an error

occurs. Instead the errors are simply acknowledged

and counted.

There is no mechanism to pull the

device off the bus if there are too many errors. If this

behavior is desired it must be implemented in the

application.

The Activity interrupt is left disabled until the USB

peripheral detects no bus activity for 3 mS. Then it

suspends the USB peripheral and enables the activity

interrupt.

The activity interrupt then reactivates the

USB peripheral when bus activity resumes so process-

ing may continue.

CheckSleep is a separate call that takes the bus idle

one step further and puts the device to sleep if the

USB peripheral has detected no activity on the bus.

This powers down most of the device to minimal cur-

rent draw.

This call should be made at a point in the

main loop where all other processing is complete.

10.9.6

EXAMPLES

This example shows how the USB functions are used.

This example first initializes the USB peripheral which

allows the host to enumerate the device. The enumer-

ation process occurs in the background, via an Inter-

rupt service routine.

This function waits until

enumeration is complete, and then polls EP1 OUT to

see if there is any data available. When a buffer is

available, it is copied to the IN buffer. Presumably your

application would do something more interesting with

the data than this example.

; ******************************************************************

; Demo program that initializes the USB peripheral, allows the Host

;

to Enumerate, then copies buffers from EP1OUT to EP1IN.

; ******************************************************************

main

call

InitUSB

; Set up everything so we can enumerate

ConfiguredUSB

; wait here until we have enumerated.

idleloop

call

CheckSleep

; Ok, here’s a good point to put part to sleep if no activity on the bus.

CheckEP1

; Check Endpoint 1 for an OUT transaction

bcf

STATUS,IRP

; point to lower banks

movlw

buffer

movwf

FSR

; point FSR to our buffer

movlw

; check end point 1

call

GetUSB

; If data is ready, it will be copied.

btfss

STATUS,C

; was there any data for us?

goto

idleloop

; Nope, check again.

PutBuffer

bcf

STATUS,IRP

; point to lower banks

movwf

bufferlen

; save buffer length

movlw

buffer

movwf

FSR

; point FSR to our buffer

swapf

bufferlen,w

; upper nybble of W is buffer length

iorlw

; lower nybble of W is EndPoint number

call

PutUSB

btfss

STATUS,C

; was it successful?

goto

PutBuffer

; No: try again until successful

goto

idleloop

; Yes: restart loop

end

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