Rabbit 6000 User’s Manual
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27.1.2 Registers
The Open Host Controller Interface (OHCI) registers use I/O addresses ranging from 0x1000 to 0x1057.
The official specification,
OpenHCI Open Host Controller Interface Specification for USB
, con-
tains full details of the registers and their proper use, and is available from Compaq.
27.2 Dependencies
27.2.1 I/O Pins
The USB port interface has four dedicated signal pins and two optional ones that are shared with parallel
port pins, all of which are listed in Table 27-1.
27.2.2 Clocks
The network port requires a 48 MHz clock input for proper full-speed USB operation. A 48 MHz crystal
can be attached between XTL_48MI and XTL_48MO, or a 48 MHz clock can be applied directly to
XTL_48MO.
The USB peripheral has a fixed 250ns access time, so wait states are usually necessary when accessing it
from the Rabbit 6000. The required number of wait states can be determined by dividing 250ns by the
period of the main clock and rounding up. NDWR is used to select between 0-63 wait states. The 250nS
cycle time for the USB peripheral comes from the 48MHz USB clock (it is twelve cycles of this clock per
access).
Register Name
Mnemonic
I/O Address
R/W
Reset
USB Wrapper Register
USBWR
0x1060
R/W
00000010
Network Port D Wait Register
NDWR
0x0433
R/W
00000000
Table 27-1. Network Port D Interface
Section
Signal
Direction
Function
Data
D+
Bidirectional Differential data
D-
Clock
XTL_48MI
—
48 MHz crystal input /
external clock input
XTL_48MO
Optional
Control
USB_PWR (PE2)
Output
External USB power control
USB_OVR (PE3)
Input
Overcurrent fault signal
Summary of Contents for 6000
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