1 circuit operation – Cirrus Logic EDB9307A User Manual
Page 11
EDB9307A
Technical Reference Manual
DS667DB1
©
Copyright 2006 Cirrus Logic, Inc.
11
4.1 Circuit Operation
The major circuit operation for each page of the schematic will be discussed.
for the latest board schematics. Look under the download link at the top of the
page.
Page 1
Block diagram and revision history.
Page 2
There are two main clock inputs to the EP9307 device. One is the 14.7456 MHz crystal oscillator and the
other is the 32.768 kHz real time clock (RTC).
The 14.7456 MHz clock can be generated from a crystal circuit as shown in the schematics, or optionally
from a 14.7456 MHz oscillator. If a 14.7456 MHz oscillator is used, then only the XTALI pin is driven and
the drive level of the clock must be 3.3 V.
The RTC clock may be generated by the circuit shown in the schematics, or optionally an RTC oscillator.
Due to the cost of RTC oscillators, the circuit shown in the schematics is used. An external oscillator is
made by using an unbuffered '04 inverter. It is very important to use an unbuffered inverter in this
application. Using a buffered inverter may make the circuit oscillate in the ~MHz range or not start at all.
Refer to application note AN265.
The two LEDs connected to the EP9307 device are used to indicate processor health during boot and
general status of the board.
The reset output, RSTON (active-low signal) is buffered by U25. There is a resistor option for the RSTON
signal to be either driven by this buffer or bypassed. If the reset signal is not going to be buffered, U25
must be removed and R117 installed. By default, RSTON is buffered.
Page 3
This block shows the peripheral connections from the EP9307 processor.
Page 4
Main items on this page are the USB 2.0 Full-speed Host, USB power, UART, and Commercial IR (CIR)
circuits.
The USB Host circuits are connected directly from the EP9307 to U3 and U4 and then on to the stacked
USB connector, J1. U3 and U4 provide termination for the USB signals and ESD protection. Note that
only two of the three USB ports are routed to USB connectors, the remaining USB port is routed to the
Peripheral Expansion header. Power for the USB Host ports comes from the +5V switching regulator and
is protected with poly fuses rated for 0.5 A each.
The board has all three UARTs brought out. The main UART interface, UART0, is connected to a
standard male DB9 connector and provides for full modem control. The other two UART interfaces are
connected to 5x2 headers. There is an option for installing zero-ohm resistors if the developer needs to
provide +5V power to an external device. The pinout of the headers matches common IDC10-to-DB9
cables. Two such cables are included with the kit. All UART signals are level shifted from TTL to RS-232.
The CIR uses an enhanced GPIO (EGPIO) line to communicate to the EP9307 device.