MAXQ612/MAXQ622 User’s Guide
12-2 Maxim Integrated
SECTION 12: UNIVERSAL SERIAL BUS (USB) INTERFACE
Note: This section only applies to the MAXQ622.
The MAXQ622 provides a USB 2.0 full-speed interface compliant with the Universal Serial Bus Revision 2.0
Specification. The full-speed USB transceiver provides a complete USB interface between the MAXQ622 and a host
USB controller. The MAXQ622 internally generates the USB clock from the 12MHz input.
Firmware libraries are available for the MAXQ622 that support the Windows
®
standard HID interface for plug-and-play
compatibility without the necessity of loading any drivers on the USB host device (PC). The USB controller described
in this document is compliant with USB Revision 2.0 Specification full-speed operation. The USB specification can be
found on www.usb.org.
The USB controller allows the MAXQ-based microcontroller to function as a full-speed USB peripheral device. The
CPU communicates to the USB controller chip through the SFR interface. The MAXQ622 provides a USB serial inter-
face engine (SIE) that, through connection to the internal USB transceiver, allows the microcontroller to function as a
USB 2.0-compliant full-speed device. The USB SIE on the MAXQ622 implements four endpoints, each with single- or
double-buffered, 64-byte data storage.
12.1 USB SIE Endpoint Description
1) EP0: Mandatory bidirectional control-type endpoint with a single-buffered, 64-byte data buffer
2) EP1: Output bulk- or INT-type endpoint with a double-buffered, 64-byte data buffer
3) EP2: Input bulk- or INT-type endpoint with a double-buffered, 64-byte data buffer
4) EP3: Input bulk- or INT-type endpoint with a single-buffered, 64-byte data buffer
Note that all endpoint directions are from the host standpoint, so an input endpoint writes data out to the host. Double-
buffering EP1 and EP2 improves throughput by allowing the CPU to read or load the next packet while the USB control-
ler is moving the current packet over USB. EP3-IN is intended to serve as a large interrupt endpoint for various USB
class specifications such as the Still Image Capture Device. It can also be used as a second bulk-IN endpoint.
Figure 12-1. MAXQ622 USB Connection
Figure 12-2. USB Interface
Windows is a registered trademark of Microsoft Corp.
MAXQ622
V
DD
V
DDB
V
BUS
V
DDIO
D-
REG18
GND
BATTERY
D+
VBUS
D-
D+
GND
MAXQ
CPU
USB
HOST
USB
CONTROLLER
(FUNCTION)
USB
TRANSCEIVER
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