PIC16C745/765
REGISTER 10-12: BUFFER DESCRIPTOR BYTE COUNT (BDndBC: 1A1h, 1A5h, 1A9h, 1ADh, 1B1h,
1B5h))
U-X
—
U-X
—
U-X
—
U-X
—
R/W-X
BC3
R/W-X
BC2
R/W-X
BC1
R/W-X
BC0
R = Readable bit
W = Writable bit
bit7
bit0
U = Unimplemented bit,
read as ‘0’
-n = Value at POR reset
X = Don’t care
bit 7-4: Reserved: Read as ’X’.
bit 3-0: BC<3:0>: The Byte Count bits represent the number of bytes that will be transmitted for an IN TOKEN or
received during an OUT TOKEN. Valid byte counts are 0 - 8. The SIE will change this field upon the com-
pletion of an OUT or SETUP token with the actual byte count of the data received.
REGISTER 10-13: BUFFER DESCRIPTOR ADDRESS LOW (BDndAL: 1A2h, 1A6h, 1AAh, 1AEh,
1B2h, 1B6h)
R/W-X
BA7
R/W-X
BA6
R/W-X
BA5
R/W-X
BA4
R/W-X
BA3
R/W-X
BA2
R/W-X
BA1
R/W-X
BA0
R = Readable bit
W = Writable bit
bit7
bit0
U = Unimplemented bit,
read as ‘0’
-n = Value at POR reset
X = Don’t care
bit 7-0: BA<7:0>: Buffer Address. The base address of the buffer controlled by this endpoint. The upper order bit
address (BA8) of the 9-bit address is assumed to be 1h. This value must point to a location within the dual
port memory space (1B8h - 1DFh). The upper order bits of the address are assumed to point to Bank 3.
Note 1: This register should always contain a value between B8h-DFh.
10.6.1 ENDPOINT BUFFERS
10.7.1.1 VUSB Output
Endpoint buffers are located in the Dual Port RAM
area. The starting location of an endpoint buffer is
determined by the Buffer Descriptor.
The VUSB provides a 3.3V nominal output. This drive
current is sufficient for a pull-up only.
10.8
USB Software Libraries
10.7
TRANSCEIVER
Microchip Technology provides a comprehensive set
of Chapter 9 Standard requests functions to aid devel-
opers in implementing their designs. See Microchip
Technology’s website for the latest version of the soft-
ware libraries.
An on-chip integrated transceiver is included to drive
the D+/D- physical layer of the USB.
10.7.1 REGULATOR
A 3.3V regulator provides the D+/D- drives with power.
A +20% 10nF capacitor is required on VUSB for regula-
tor stability.
TABLE 10-1: USB PORT FUNCTIONS
Input
Type
Output
Type
Name
Function
Description
VUSB
VUSB
D-
—
Power
USB
3.3V for pull up resistor
USB Differential Bus
USB Differential Bus
D-
USB
USB
D+
D+
USB
Legend:
OD = open drain, ST = Schmitt Trigger
DS41124A-page 70
Advanced Information
1999 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
