PRU Cape Hardware User Guide

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Introduction

This document describes the hardware architecture of the PRU Cape  which is compatible with the Beagle Bone Black development platform. 


Description

The PRU Cape is a test, development, and evaluation module system that enables developers to write software and develop hardware around the PRU subsystem. Examples of basic I/O such as push buttons and LEDs as well as more complicated examples such as audio and 1-Wire for temperature sensing are available on this cape to showcase what the PRU can accomplish in terms of inputs and outputs.

The following sections give more details regarding the PRU Cape.



EVM System View

The PRU Cape is shown below in Figure 1.

PCB_Angle.PNG
Figure 1: PRU Cape Angle



Schematics/Design/Errata Files

  • Design Files (located under Technical Documents), includes:
- Schematic
- Layout
- Assembly Drawings
- CAD Files
- Bill of Materials (BOM)
- I2C SCL and SDA signals swapped (REV 1.2A)
The AM335x I2C2_SDA signal (routed to BBB Header P9-20) is connected to the EEPROM SCL pin. The AM335x I2C2_SCL signal (routed to BBB Header P9-19) is connected to the EEPROM SDA pin. The EEPROM is blank, and if it is to be used, the cape needs to be modified to physically swap the SDA and SCL signals.



System Description

System Board Diagram

The system block diagram of the PRU Cape are shown in Figure 2 and Figure 3.



Board_Layout.JPG System_Diagram.JPG
Figure 3: PRU Cape Board Layout
Figure 4: PRU Cape Functional Block Diagram


Signals Used 


Table 1. Signals Used
CAPE NAME BBB HEADER NUMBER BBB MODE 0 NAME CAPE USE
PR1_PRU0_GPO0 P9-31 MCASP0_ACLKX PRU0 Blue LED
PR1_PRU0_GPO1 P9-29 MCASP0_FSX PRU0 Green LED
PR1_PRU0_GPO2 P9-30 MCASP0_AXR0 PRU0 Orange LED
PR1_PRU0_GPO3 P9-28 MCASP0_AHCLKR PRU0 Red LED
PR1_PRU1_GPO3 P8-44 LCD_DATA3 PRU1 Blue LED
PR1_PRU1_GPO4 P8-41 LCD_DATA4 PRU1 Green LED
PR1_PRU1_GPO5 P8-42 LCD_DATA5 PRU1 Red LED
PR1_PRU0_GPI7 P9-27 GPIO3_19 SW1
PR1_PRU0_GPI5 P9-25 GPIO3_21 SW2
PR1_PRU1_GPO0 P8-45 LCD_DATA0 Audio Data
PR1_PRU1_GPO1 P8-46 LCD_DATA1 Audio Clock
PR1_PRU1_GPO2 P8-43 LCD_DATA2 Audio Sync
PR1_UART0_TXD P9-24 UART1_TXD UART TxD
PR1_UART0_RXD P9-26 UART1_RXD UART RxD
PR1_UART0_RTS P9-21 UART2_TXD UART RTS
PR1_UART0_CTS P9-22 UART2_RXD UART CTS
PR1_PRU_EDIO_DATA_OUT6 P8-39 LCD_DATA6 LCD RS
PR1_PRU_EDIO_DATA_OUT4 P8-28 LCD_PCLK LCD E
PR1_PRU_EDIO_DATA_OUT0 P9-18 I2C1_SDA LCD Data4
PR1_PRU_EDIO_DATA_OUT1 P9-17 I2C1_SCL LCD Data5
PR1_PRU_EDIO_DATA_OUT2 P8-27 LCD_VSYNC LCD Data6
PR1_PRU_EDIO_DATA_OUT3 P8-29 LCD_HSYNC LCD Data7
PR1_PRU_EDIO_DATA_OUT5 P8-30 LCD_DE HDQ input
PR1_PRU0_GPI14 P8-16 GPIO1_14 HDQ output
I2C2_SDA P9-20 I2C2_SDA I2C SCL
I2C2_SCL P9-19 I2C2_SCL I2C SDA
PR1_ECAP0_IN_PWM0_OUT P9-42 ECAP0_IN_PWM0_OUT ECAP0_IN_PWM0_OUT
PR1_PRU0_GPI15 P8-15 GPMC_AD15 PRU0_GPI_15
VDD_3V3C P9-3, P9-4  VDD_3V3C VDD_3V3C
DGND P8-1, P8-2, P9-1,P9-2 DGND DGND
DGND P9-43, P9-44, P9-45, P9-46 DGND DGND





PRU Cape Functional Block Descriptions

This section describes major functional blocks of the PRU Cape.


Audio 

The audio portion of the PRU Cape is composed of a Dual 8-bit DAC (DAC082S085) and a dual 105 mW Amplifier (LM4808). The output is then sent to a 3.5 mm Audio jack with a max pk-pk of .89V, following the consumer standard.


CAPE NAME BBB HEADER NUMBER BBB MODE 0 NAME CAPE USE
PR1_PRU1_GPO0 P8-45 LCD_DATA0 Audio Data
PR1_PRU1_GPO1 P8-46 LCD_DATA1 Audio Clock
PR1_PRU1_GPO2 P8-43 LCD_DATA2 Audio Sync


EEPROM

The EEPROM on the PRU cape is the CAT24C256WI-G EEPROM 256Kb I2C SOIC8, and has an attached DIP switch to manipulate the I2Caddress. The first 78 bytes hold a file that the Beagle Bone Black will read to identify the cape, the rest of the EEPROM is available for use.


CAPE NAME BBB HEADER NUMBER BBB MODE 0 NAME CAPE USE
I2C2_SDA              P9-20 I2C2_SDA I2C SCL           
I2C2_SCL P9-19 I2C2_SCL I2C SDA

eCAP 

These pins are brought out on the board that connect to the eCAP0 PWM0 IN to allow use of the PRU Subsystem's eCAP IP.


CAPE NAME BBB HEADER NUMBER BBB MODE 0 NAME CAPE USE
PR1_ECAP0_IN_PWM0_OUT P9-42 ECAP0_IN_PWM0_OUT ECAP0_IN_PWM0_OUT
PR1_PRU0_GPI15 P8-15 GPMC_AD15 PRU0_GPI_15

 

LCD 

The LCD screen is on a duaghter board with its own built in controller, model number  NHD-0208AZ-RN-YBW-33V. The LCD is connected to the PRU Cape throught the 2x8 female header in the middle of the cape. The LCD is a 2x8 Character display operating at 3.3V.


Cape Name BBB Header Number BBB Mode 0 Name Cape Use
PR1_PRU_EDIO_DATA_OUT6 P8-39 LCD_DATA6 LCD RS
PR1_PRU_EDIO_DATA_OUT4 P8-28 LCD_PCLK LCD E
PR1_PRU_EDIO_DATA_OUT0 P9-18 I2C1_SDA LCD Data4
PR1_PRU_EDIO_DATA_OUT1 P9-17 I2C1_SCL LCD Data5
PR1_PRU_EDIO_DATA_OUT2 P8-27 LCD_VSYNC LCD Data6
PR1_PRU_EDIO_DATA_OUT3 P8-29 LCD_HSYNC LCD Data7


LEDs

The PRU Cape has 7 surface mounted LEDs, including Red, Orange, Blue and Green colors. There are 4 LEDs connected to PRU0 output, and 3 connected to PRU1 output.


CAPE NAME BBB HEADER NUMBER BBB MODE 0 NAME CAPE USE
PR1_PRU0_GPO0 P9-31 MCASP0_ACLKX PRU0 Blue LED
PR1_PRU0_GPO1 P9-29 MCASP0_FSX PRU0 Green LED
PR1_PRU0_GPO2 P9-30 MCASP0_AXR0 PRU0 Orange LED
PR1_PRU0_GPO3 P9-28 MCASP0_AHCLKR PRU0 Red LED
PR1_PRU1_GPO3 P8-44 LCD_DATA3 PRU1 Blue LED
PR1_PRU1_GPO4 P8-41 LCD_DATA4 PRU1 Green LED
PR1_PRU1_GPO5 P8-42 LCD_DATA5 PRU1 Red LED




Switches

The PRU Cape has two pushbutton switches connected to PRU0 inputs.


CAPE NAME BBB HEADER NUMBER BBB MODE 0 NAME CAPE USE
PR1_PRU0_GPI5 P9-27 GPIO3_19 SW1
PR1_PRU0_GPI7 P9-25 GPIO3_21 SW2




Temperature Sensor

The temperature sensor is a MAX31820 ambient temperature sensor, with a 1-Wire interface. Two pins are tied together from the PRU to create input and output on a single wire.


CAPE NAME BBB HEADER NUMBER BBB MODE 0 NAME CAPE USE
PR1_PRU_EDIO_DATA_OUT5 P8-30 LCD_DE HDQ input
PR1_PRU0_GPI14 P8-16 GPIO1_14 HDQ output



Test Space

The test space is a set of 150 through holes (15x10). There is no connection between the through holes and is meant for attaching a through hole component, wheather it be an IC or passive to test with the PRU or any signal that can be accessed through the Cape Headers.



UART

There is one RS-232 connector (DB9 male) on the PRU Cape. The MAX3232ECD is the line driver/receiver.


CAPE NAME BBB HEADER NUMBER BBB MODE 0 NAME CAPE USE
PR1_UART0_TXD P9 24 UART1_TXD UART TxD
PR1_UART0_RXD P9 26 UART1_RXD UART RxD
PR1_UART0_RTS P9 21 UART2_TXD UART RTS
PR1_UART0_CTS P9 22 UART2_RXD UART CTS



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