Datasheet

 1999-2013 Microchip Technology Inc. Preliminary DS41124D-page 71
PIC16C745/765
REGISTER 10-13: BUFFER DESCRIPTOR ADDRESS LOW
(BDndAL: 1A2h, 1A6h, 1AAh, 1AEh, 1B2h, 1B6h)
10.6.1 ENDPOINT BUFFERS
Endpoint buffers are located in the Dual Port RAM
area. The starting location of an endpoint buffer is
determined by the Buffer Descriptor.
10.7 Transceiver
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,
as well as an external pin. This pin is intended to be
used to power a 1.5k +
5% pull-up resistor on the D-
line to signal a low speed device, as specified by the
USB 1.1 Specification. A +20% 200nF capacitor is
required on V
USB for regulator stability.
FIGURE 10-2: EXTERNAL CIRCUITRY
10.7.1.1 VUSB Output
The V
USB provides a 3.3V nominal output. This drive
current is sufficient for a pull-up only.
10.8 USB Software Libraries
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.
TABLE 10-1: USB PORT FUNCTIONS
R/W-X R/W-X R/W-X R/W-X R/W-X R/W-X R/W-X R/W-X
BA7 BA6 BA5 BA4 BA3 BA2 BA1 BA0 R = Readable bit
W = Writable bit
U = Unimplemented bit,
read as ‘0’
-n = Value at POR reset
X = Don’t care
bit7 bit0
bit 7-0: 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, Bank 3 (1B8h - 1DFh).
Note 1: This register should always contain a value between B8h-DFh.
PIC16C745/765
Host
Controller/HUB
V
USB
D-
D+
200 nF
APPLICATION
Note: The PIC16C745/765 requires an external resistor and
capacitor to communicate with a host over USB.
1.5K
Name Function
Input
Type
Output
Type
Description
V
USB VUSB — Power Regulator Output Voltage
D- D- USB USB USB Differential Bus
D+ D+ USB USB USB Differential Bus
Legend: OD = open drain, ST = Schmitt Trigger