PXA3xx Design Guide - Marvell

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PXA3xx Processor FamilyDesign GuideFigure 86: Consumer Infrared Unit Connection ExamplePXA3xxProcessorCIR ControllerCIR_OUTR124.4 Layout NotesThe maximum specified switching speed of the CIR is 7.43 MHz, but applications use significantlylower carrier (switching) rates. For example, RC5 uses a 36 kHz carrier frequency. At this speed,degradation of signal integrity is not likely to occur. But, the use of the best possible design androuting practices is still encouraged.Follow these recommendations when routing signals to ensure the most reliable design possible:• Keep the signal trace as short as possible.• Route the signal with as much of the trace on an inner signal layer as possible.• The traces supplying power to the IR LED/drive transistor/current limit resistor should be sizedto accommodate the current driven through the IR LED.Doc. No. MV-S301368-00 Rev. A Copyright © 2009 MarvellPage 192April 6, 2009, Released
25 Pulse-Width Modulator Interface25.1 Overview25.2 SignalsThe PXA3xx processor family pulse-width modulator (PWM) interface contains four pins that can beconfigured to generate periodic output signals. Configuration of the PWMs is accomplished throughsoftware and is described in detail in Marvell ® PXA30x, PXA31x, and PXA32x Processors Vol. IV:Serial Controller Configuration Developers Manual, “Section 9: Pulse-Width Modulator Controller”.PWM signals are implemented through GPIOs. Therefore, the hardware considerations necessaryfor the PWM signals are the same as that of the GPIOs.The PWM signals are implemented through the GPIOs of the PXA3xx processor family. Refer to theGPIO alternate-function table in Marvell ® PXA30x, PXA31x, and PXA32x Processors Vol. I: Systemand Timer Configuration Developers Manual , “Section 5: General-Purpose I/O Unit” for the GPIOassignments of the PWM signals.See Table 81 for the list of signals controlled by the PWM controller of the PXA3xx processor family.Table 81:PWM Interface Signal ListSignal Name Type DescriptionPWM_OUT0 Output Pulse-width modulated output signal for PWM0PWM_OUT1 Output Pulse-width modulated output signal for PWM1PWM_OUT2 Output Pulse-width modulated output signal for PWM2PWM_OUT3 Output Pulse-width modulated output signal for PWM325.3 Block DiagramThe connection of the PWM to the peripheral device using the PWM is typically direct. However, ifthe PWM is used as a software-controlled voltage source, a low-pass filter must be placed in line. Anexample of a software controlled voltage source is for the contrast control on an LCD panel. If thePWM output is used for generating audio, an appropriate filter is also required. In this case, the filteris a band-pass filter.The specification and design of the filter depends on the exact purpose of the application. See theblock diagram for a design requiring a low-pass or band-pass filter in Figure 87.Copyright © 2009 MarvellDoc. No. MV-S301368-00 Rev. AApril 6, 2009, Released Page 193
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PXA3xx Design Guide - Marvell

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