How-To: Bussepiraten, Universal Serial Interface

Oppdatering: Ny firmware med JTAG og mer

Vi er alltid ekstatisk for å få en ny chip eller SIM-kort til grensesnitt, men vår entusiasme er vanligvis dempet av prototypingsprosessen. Interfacing Enhver chip indikerer normalt at brødbrettet en krets, skriver kode og henter programmereren; kanskje til og med en prototyping PCB.

For noen år siden bygget vi den første “busspiraten”, et universelt bussgrensesnitt som snakker med mange sjetonger fra en PC-seriell terminal. Flere konvensjonelle serielle protokoller støttes til 3,3-5volt, inkludert I2C, SPI og asynkron seriell. Ytterligere ‘Raw’ 2- og 3-Wire-biblioteker kan grensesnitt nesten alle proprietære serielle protokoller. Tatt i betraktning at dette har vært et så gunstig verktøy for oss, renset vi opp koden, dokumenterte designet, og utgav det her med spesifikasjoner, skjematisk og kildekode.

Konseptoversikt

Busspiraten er en seriell terminalbro til flere IC-grensesnittprotokoller. Vi skriver kommandoer i en seriell terminal på datamaskinen. Kommandoene går til busspiraten gjennom PC-serien. Busspiraten snakker til en mikrochip i riktig protokoll, og returnerer resultatene til PCen.

Alle pins utgang 3.3volts, men er 5volt tolerante. PER-board 3.3volt og 5volt strømforsyninger er tilgjengelig for å drive den tilkoblede brikken. Programvare konfigurerbare I2C pull-up motstander fullfører pakken.

Det serielle terminalgrensesnittet fungerer med et hvilket som helst system: PC, Mac, Linux, Palm-piloter, Wince-enheter, etc; Ingen crapware kreves. Vi betraktet som en USB-enhet, men USB er ikke kompatibel med det vesentlige antall håndholdte enheter som har en seriell port. Vi ønsket også en 3.3volt-enhet med 5volt tolerante innganger, men mange populære gjennom-hulls USB-mikrokontoller var 5volt-deler (f.eks. PIC18FX550).

Busspiraten “snakker for øyeblikket” Tre maskinvareprotokoller for høyhastighetsgrensesnitt, og har to programvareprotokollbiblioteker for enkel bussmanipulering. Teorien og spesifikasjonen til hver protokoll er utenfor det vi kan dekke her, men sjekk ut noen av disse opplæringene:

I2c.

En langsom 2 wire buss. Wikipedia er et kjempefint sted å starte for I2C bakgrunn. I2C-Bus.org, Robotelektronikk, Embedded Systems Academy, og Embedded.com har respektabel I2C-opplæringsprogrammer.

Spi.

En grunnleggende 3 wire buss. Wikipedia har bakgrunn; Embedded.com har en fantastisk opplæring og sammenligning med I2C.

Universal Asynkron mottaker sender (UART eller Serial)

En klokke og timingavhengig seriell protokoll som er best kjent for utseendet som PC-seriell portprotokoll. Wikipedia har bakgrunn på asynkron serielle protokoller.

RAW 2 Wire.

Dette er et generisk 2 wire protokollbibliotek, som ligner i2c, men uten en ACK-bit. I2C og mange proprietære 2-trådprotokoller kan dannes ved hjelp av bussmanipulasjonene som er tilgjengelige i denne modusen. Bruk dette biblioteket til å jobbe med ikke-I2C 2-trådenheter, som SmartCards eller Sensirion SHT11 temperatur / fuktighetssensorer.

RAW 3 Wire.

Dette er et generisk 3 wire protokollbibliotek, som ligner SPI, men uten begrensninger av en maskinvaremodul. Bruk dette biblioteket til å jobbe med enheter som bruker ikke-8bit-kompatible 3-tråds protokoller, som SPARKFUN Nokia 6100 LCD Knock-off. Mange 3 trådprotokoller kan dannes ved hjelp av bussmanipulasjonene som er tilgjengelige i denne modusen.

Maskinvare

Klikk for en full størrelse PCB-plasseringsbilde (PNG). Skrueterminaler Koble til strømforsyningene. En rad med syv pin-overskrifter forbinder i IO-pinnene. Til tross for etiketten er det bare 7volts DC påkrevd.

Pin

Spi.

I2c.

RS232.

B9.

Mosi.

SDA.

–

B8.

CLK.

Scl.

–

B7.

Miso.

–

RX.

B6.

CS.

–

Tx.

B5.

AUX.

AUX.

AUX.

Bakke

GND.

GND.

GND.

Denne tabellen viser PIN-tilkoblingene for hver bussmodus. RAW 2 Wire-modus bruker samme PIN-konfigurasjon som I2C. Raw 3 Wire-modus bruker samme PIN-konfigurasjon som SPI.

Klikk for en full størrelse kretsbilde (PNG). Kretsen og PCB er opprettet ved hjelp av freeware-versjonen av Cadsoft Eagle. Last ned prosjektarkivet (ZIP).

PIC 24FJ64GA002.

Vi brukte en PIC24FJ64GA002 mikrokontroller i bussen pirat; Dette er den samme brikken vi brukte i vårt mini-serverprosjekt. It’s fast enough to do everything we want (16MIPS), and the peripheral pin select feature allows the hardware SPI, UART, and I2C modules to share output pins. Each power pin needs a decoupling capacitor(C12,13), and the MCLR function requires a resistor (R7) between pin 1 and 3.3volts. The photo has an internal voltage regulator that requires a 10uF tantalum capacitor (C3), though we used a plain electrolytic capacitor without issue. read about programming and working with this chip in our PIC24F tutorial. If you don’t have a photo debugger, several readers recommend the under-$40 ICD2 clones on eBay.

The photo runs at 3.3volts, but the digital-only pins are 5volt tolerant for interfacing 5volt logic. Pins 14,15,16,17,18,21, and 22, are digital only, which we figured out by looking through the datasheet and eliminating any pins with an analog connection type (table 1-2, pages 11-16). According to the datasheet,I2C pins are also 5volt tolerant. There’s a bunch of conflicting information on the web, but datasheet page 230, parameter DI28, clearly states that the max input for a 24FJ64GA002 I2C pin without analog circuitry is 5.5volts.

Pins 21 and 22 (RB10/11) can pull-up SDA/SCL through resistors R4 and R5.

MAX3223CPP

This chip converts 3.3volt serial output to +/-10volt RS232 signals compatible with a PC serial port. The MAX3223CPP is a 3-5volt version of the MAX202, with extra power saving features. MAX RS232 transceivers require four 0.1uF capacitors for a charge pump (C4,5,7,8), and one decoupling capacitor (C17). We used the same capacitors for everything.

We used a MAX3223CPP, which doesn’t seem to be available anymore. MAX3223EEPP+ is a pin-compatible newer version, available at Digikey for $7. Au! None of the 3223’s power saving features are used, so a cheaper, simpler 3.3volt RS232 transceiver must be substituted if in any way possible.

Strømforsyninger

Most chips can be powered from the Bus Pirate’s on-board 3.3volt and 5volt supplies. 5volts is supplied by a common 7805 regulator (VR2) and two decoupling capacitors (C9,10). An LM317 adjustable regulator (VR1) is set to 3.3volts using two resistors (R2,3), and requires two decoupling capacitors (C6,7). The circuit requires a 7-10volt DC supply (J1).

Deleliste

Del
Verdi

IC1
PIC24FJ64GA002-DIP

IC2
MAX3223CPP (try MAX3223EEPP+)

C3
10uF capacitor (preferably tantalum)

C4-13,17
0.1uF capacitors

R1
330 ohm resistor

R2
240 ohm resistor

R3
390 ohm resistor

R4,5,7
2K2 ohm resistor

VR1
LM317

VR2
LM7805

X1
Screw clamp (3 terminals) *untested

X2
DB9 female connector (serial port) *untested

ICSP,SV3
.1″ pin header, ideal angle

J1
Power jack, 2.1mm pin

LED1
3mm LED (optional)

Firmware

The firmware is written in C using the complimentary demonstration version of the photo C30 compiler. learn all about working with this photo in our introduction to the photo 24F series. Last ned prosjektarkivet (ZIP).

main.c – Handles the user terminal interface.

busPirate.c – Abstraction routines that convert syntax to actions on the proper bus.

uartIO.c – IO routines for both hardware UARTs.

m_i2c_1.c – software I2C routines by [Michael Pearce]. We couldn’t get the photo hardware I2C to work, so we used this valuable library. The software doesn’t take into account the I2C speed setting, and seems to work at about 5KHz.

SPI.c – routines that drive the hardware SPI module.

raw2wire.c – software 2-wire interface library.

raw3wire.c – software 3-wire (SPI) interface library.

User input is held in a 4000 byte buffer until a newline character (enter) is detected. If the first character of the input is a menu option (see below), the menu dialog is shown, otherwise the string is parsed for data to send over the bus (see syntax). The code consists of an embarrassing number of switch statements and spaghetti code.

Terminal interface

Rather than write a junk piece of software to control the device, we gave it a serial command line interface that will work with any ASCII terminal.  The bus pirate responds to commands with three digit result codes and a short message. The codes are created with PC automation in mind. We’ve included a table of result codes in the project archive (zip).

Menu options

Menu options are single character commands that don’t involve data transfers. enter the character, followed by , to access the menu.

? – show a help menu with commands and syntax.

M – set the bus mode (SPI, I2C, UART, raw 2 wire, raw 3 wire). followed right away by a prompt for speed, polarity, and output state (mode dependent).

Bus speeds: SPI:30, 125, 250, 1000KHz. I2C:100, 400, 1000KHz. UART: 300, 1200, 2400, 4800, 9600, 19200, 38400, 57600, 115200bps. Raw modes: 1, 10, 50KHz.

Inverse clock setting sets the idle state opposite of normal (normal SPI:idle low; normal UART:idle high): SPI:idle high; UART:idle low.

Some modes have optional high-z output modes for use with pull-up resistors (Low=ground, High=input).

L – Toggle bit transmit/receive order: most/least significant bit first.

P – SDA/SCL pin pull-up resistor toggle (3.3volts). only valid in I2C and raw 2 wire modes.

O – set number output display format. The terminal can display numbers as decimal, hexadecimal, and binary ASCII values. A fourth format sends the raw, unprocessed byte for reading ASCII formatted text.

Syntax

A basic syntax is used to communicate with chips over a bus.  Syntax commands have generic functions that normally apply to all bus types.

A/a/@ – Toggle auxiliary pin. capital “A” sets AUX high, small “a” sets to ground. @ sets aux to input (high impedance mode) and reads the pin value.

[ – start data write. SPI/raw 3 wire: chip select enabled. I2C/raw 2 wire: start condition. RS232: open UART, discard received bytes.

{ – start data write with reads. same as [, except: SPI/raw 3 wire: show the read byte for each write. RS232: display data as it arrives asynchronously.

] or } – end data write. SPI/raw 3 wire: chip select disabled. I2C/raw 2 wire: stop condition. RS232: close UART.

R/r – read byte. SPI/raw 3 wire: send dummy byte, return read. I2C: read byte with ACK. Raw 2 wire: read 8 bits. RS232: check UART for byte and return, or fail if empty. use 0r1…255 for bulk reads up to 255 bytes.

0b – write this binary value. format is 0b00000000 for a byte, but partial bytes are also fine: 0b1001.

0h or 0x – write this HEX value. format is 0h01 or 0x01. Partial bytes are fine: 0xA. A-F can be lower-case or capital letters.

0-255 – write this decimal value. any number not preceded by 0x, 0h, or 0b is interpreted as a decimal value.

, or space – Value delimiter. use a coma or space to separate numbers. any combination is fine, no delimiter is required between non-number values: {0xa6,0, 0 16 5 0b111 0haF}.

Direct bus manipulation commands for raw 2 wire mode and raw 3 wire mode.
^ – send one clock tick. use 0^1…255 for multiple clock ticks.

/ and \ – Toggle clock level high (/) and low (\). includes clock delay (100uS).

-/_ – Toggle data state high (-) and low (_). includes data setup delay (20uS).

! – read one bit with clock.

. – read data pin state (no clock).

& – delay 1uS. use 0&1…255 for multiple delays.

Bruker det

Here are two examples that show the Bus Pirate in action. Terminals must be set to ASCII mode with local echo, we used the Windows serial terminal. The PC-side serial connection is 115200bps, 8N1. The Bus Pirate must respond to any single line feed type (0x0a, 0x0d), or both (Windows style).

.I2C/SPI – Flash 24LC1025 EEPROM

Microchip’s EEPROMS are popular permanent-storage memory chips, the 24LC1025 has 128Kbytes of storage with an I2C interface.  We can test this chip without bread-boarding a big circuit or writing code.

The picture shows an 24LC1025 connected to the Bus Pirate. The EEPROM works from 2.7 to 5volts, so we used the 3.3volt supply from the Bus Pirate to power the circuit. The on-board SDA/SCL pull-up resistors hold the I2C bus high, and eliminate the need for external resistors. A single 0.1uF capacitor decouples the EEPROM from the power supply.

Setup I2C mode

First, we setup the Bus Pirate for I2C mode and enable the pull-up resistors. considering that the Bus Pirate currently uses a software I2C library, the speed setting doesn’t really have an effect.

SPI>m  <–enter m for mode select 1. SPI 2. I2C 3. UART 4. RAW 2 WIRE 5. RAW 3 WIRE MODE>2  <–enter 2 for I2C 900 mode SET Set speed: 1. 100KHz (Standard) 2. 400KHz (Fast Mode) 3. 1MHz (High Speed) SPEED>1 <–speed doesn’t really do anything… 901 speed SET 202 I2C READY, P/p FOR PULLUPS I2C>P   <–enable the I2C pull-up resistors 205 I2C PULLUP ON I2c>

Write to EEPROM (I2C)

All I2C operations begin with a start condition { or [, and end with a stop condition } or ]. A write begins by addressing the device (1 byte) and trying to find an acknowledgment bit (ACK). If the EEPROM responds, we can send the data location to write (2 bytes) and data payload (n bytes). The Bus Pirate automatically checks for an ACK at the end of each write, and ACKs each read.

The 24LC1025 base address is 1010xxy, where xx is figured out by the state of pins 2 and 3, and y is read (1) or write (0) mode. We tied pins 2 and 3 high, making the full write address 1010110.  We’ll start writing to the device at the first data location (0 0), and write one to thirteen using a mix of data input formats (1…13).

I2C>{0b10100110 0 0 1 2 3 4 5 6 7 8 9 10 0xb 0xc 13} <–I2C command 210 I2C start condition <–bus start 220 I2C WRITE: 0xA6 got ACK: yes <–address sent and ACK received 220 I2C WRITE: 0x00 got ACK: yes <–write address 220 I2C WRITE: 0x00 got ACK: yes <–write address 220 I2C WRITE: 0x01 got ACK: yes <–data ... 220 I2C WRITE: 0x0D got ACK: YES 240 i2c stopp tilstand I2c>

Read from EEPROM (I2C)

Reading the 24LC1025 takes two steps. First, a write command with no data sets the address pointer. Second, a read comm