PIC16C745SLASHP datasheet(64/158 Pages) MICROCHIP

64 / 158 page

PIC16C745/765

DS41124A-page 64

Advanced Information

10.5.1.5

Status Register (USTAT)

The USB Status Register reports the transaction sta-

tus within the USB. When the MCU recognizes a

TOK_DNE interrupt, this register should be read to

determine the status of the previous endpoint commu-

nication. The data in the status register is valid when

the TOK_DNE interrupt bit is asserted.

The USTAT register is actually a read window into a

status FIFO maintained by the USB. When the USB

uses a BD, it updates the status register. If another

USB transaction is performed before the TOK_DNE

interrupt is serviced the USB will store the status of the

next transaction in the STAT FIFO. Thus, the STAT reg-

ister is actually a four byte FIFO which allows the MCU

to process one transaction while the SIE is processing

the next. Clearing the TOK_DNE bit in the INT_STAT

with the contents of the next STAT value. If the data in

the STAT holding register is valid, the SIE will immedi-

ately reassert the TOK_DNE interrupt.

USB STATUS REGISTER (USTAT: 194h)

U-0

R-X

U-0

—

ENDP1

ENDP0

—

R = Readable bit

W = Writable bit

U = Unimplemented bit,

read as ‘0’

-n = Value at POR reset

X = Don’t care

bit7

bit0

bit 7-5:

Unimplemented: Read as ’0’.

bit 4-3:

ENDP<1:0>: These bits encode the endpoint address that received or transmitted the previous token.

This allows the microprocessor to determine which BDT entry was updated by the last USB transaction.

bit 2:

IN: This bit indicates the direction of the last BD that was updated.

= The last transaction was an IN TOKEN

= The last transaction was an OUT or SETUP TOKEN

bit 1-0:

Unimplemented: Read as ’0’.

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