IPC@CHIP SC123/SC143
Hardware Manual V1.06 [18.02.2010]
©2000-2008 BECK IPC GmbH Page 38
6.6 USB
The SC1x3 supports USB 1.1. It is a serial bus operating at 12 Mbps. USB 1.1 provides an expandable, hot-
pluggable Plug-and-Play serial interface that ensures a standard, low-cost socket for connecting to USB hosts.
Version 1.1 of the USB specification provides for peripheral speeds of up to 1.5 Mbps for low-speed devices
and up to 12 Mbps for full-speed devices.
Microprocessor Interface
The SC1x3 USB interrupt is logically ORed with external interrupt 3.
The interface has an integrated DMA controller that transfers packet data to and from memory. The DMA
controller facilitates USB endpoint data transfer efficiently, while limiting microprocessor involvement.
Digital Phase Lock Loop Logic
The USB Digital Phase Lock Loop (DPLL) maintains a 12 MHz clock source that is locked to the USB data
steam. The DPLL requires a 48 MHz clock to 4x over sample the USB data stream and detect transitions.
These transitions are used to synthesize a nominally 12 MHz USB clock.
USB Pull-up/Pull-down Resistors
USB uses pull-up or pull-down resistors to determine when an attach or detach event occurs on the bus. Figure
6-16 shows the two resistor combinations required for USB Devices and Hosts.
Normally, the USB starts in Host mode (HOSTMODE = HIGH). This mode disables resistor R1 and enables the
resistors R2 and R3. HOSTMODE can be any PIO pin, configurable through the RTOS. When the USB driver is
configured to Device mode, HOSTMODE is set to LOW so, R1 pulls USBP up and a connected Host
recognizes a Full-Speed Device is attached.
The circuit shown in Figure 6-16 is important for implementing a USB Device. Without the option to
activate/deactivate the resistors, the SC1x3 will initiate the attach event at the Host, before the SC1x3 USB
driver is ready.
Figure 6-16: Pullup-/down Resistors for USB full-speed device
3.3V
3.3V
R2
15K
R3
15K
Q3
R5
1K
R1
1K5
5V
R4
10K
Q1
GND
Q2
J1
USB
1
2
3
4
R6
10K
R7
10K
GND
GND
IC2
SC1x3
N2
N1
USBP
USBN
HOSTMODE
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