3.7.5.2. PRU Cape Hardware User Guide

3.7.5.2.1. Introduction

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


3.7.5.2.1.1. 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.


3.7.5.2.1.2. EVM System View

The PRU Cape is shown below.

../../_images/PCB_Angle.PNG

3.7.5.2.2. Schematics/Design/Errata Files

Design Files (located under Technical Documents), includes:

  • Schematic

  • Layout

  • Assembly Drawings

  • CAD Files

  • Bill of Materials (BOM)

Errata

  • 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.

PRU Cape Getting Started Guide


3.7.5.2.3. System Description

3.7.5.2.3.1. System Board Diagram

The system block diagram of the PRU Cape are shown in the below Figures.


PRU Cape Board Layout:

../../_images/Board_Layout.JPG

PRU Cape Functional Block Diagram

../../_images/System_Diagram.JPG

3.7.5.2.3.2. 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

Table: Table 1. Signals Used


3.7.5.2.4. PRU Cape Functional Block Descriptions

This section describes major functional blocks of the PRU Cape.


3.7.5.2.4.1. 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


3.7.5.2.4.2. 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

3.7.5.2.4.3. 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

3.7.5.2.4.4. 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


3.7.5.2.4.5. 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


3.7.5.2.4.6. 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



3.7.5.2.4.7. 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


3.7.5.2.4.8. 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.


3.7.5.2.4.9. 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