Front I/O - XWiki

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= Pinout =

There is a single cable that controls four parts, each half side of I/O LED and center column of blue LEDs.

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[[image:xserve io main cable and PCB pinout.drawio.png||alt="xserve io main cable pinout.drawio.png"]]

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[[attach:xserve io main cable pinout.drawio.svg||target="_blank"]]

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This cable allows us to communicate with 4 chips using two data lines, audio & service switch, case switch and (yet to be documented) compute LEDs

= How we got here =

Measure out the ground and power signals by comparing with other chips on board. E.g. we find [SAA1064T] datasheet, locate the GND (Vee) and 5V (Vcc) and measure connectivity (0 ohm resistance) between chip pins and cable pins. This gives us pins GND 2 & 8 and PWR 16 & 22.

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We keep doing this for SCL & SDA pins on SAA1064T chip and find pins 14 & 15 and 20 & 21 are I2C clock and data pins for each chip.

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== Finding i2c chip address ==

=== SAA1064T ===

Reading the datasheet for SAA1064T chip we find that: "//This results in the corresponding valid addresses HEX 70, 72, 74 and 76 for writing and 71, 73, 75 and 77 for reading. All other addresses cannot be acknowledged by the circuit".// Giving us a clue what we are looking for, i2c addresses 0x70, 0x72 or 0x74.

=== PCA9554 ===

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=== Code example finding i2c addresses ===

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We can test the following addresses manually or use the following code snippet:

/*I2C_scanner

This sketch tests standard 7-bit addresses.

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Devices with higher bit address might not be seen properly.*/

#include <Wire.h>

void setup() {

Wire.begin();

Serial.begin(9600);

while (!Serial);

Serial.println("\nI2C Scanner");

}

void loop() {

byte error, address;

int nDevices;

Serial.println("Scanning...");

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nDevices = 0;

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for (address = 1; address < 127; address++ ) {

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Wire.beginTransmission(address);

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error = Wire.endTransmission();

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if (error == 0) {

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Serial.print("I2C device found at address 0x");

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if (address < 16)

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Serial.print("0");

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Serial.print(address, HEX);

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Serial.println(" !");

nDevices++;

}

else if (error == 4) {

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Serial.print("Unknown error at address 0x");

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if (address < 16)

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Serial.print("0");

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Serial.println(address, HEX);

}

}

if (nDevices == 0)

Serial.println("No I2C devices found\n");

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else

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Serial.println("done\n");

delay(5000);

}

== i2c multiplexing with TCA9548 ==

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We have two sets of chips, one for left and one for right where we have two different i2c chips on each side for controlling lights. Since the chips controlling their respective parts have the same address for each side, we can't distinguish them from each other. To handle this we use a i2c multiplexer to selectively communicate with one half at a time, switching TCA9548 between two different output ports.

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=== Code example finding i2c ports ===

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To verify wiring, connection, output ports and device addresses run the following script:

/**

* TCA9548 I2CScanner.ino -- I2C bus scanner for Arduino

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*

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* Based on https://playground.arduino.cc/Main/I2cScanner/

*

*/

#include "Wire.h"

#define TCAADDR 0x70

void tcaselect(uint8_t i) {

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if (i > 7) return;

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Wire.beginTransmission(TCAADDR);

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Wire.write(1 << i);

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Wire.endTransmission();

}

// standard Arduino setup()

void setup()

{

while (!Serial);

delay(1000);

Wire.begin();

Serial.begin(9600);

Serial.println("\nTCAScanner ready!");

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for (uint8_t t=0; t<8; t++) {

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tcaselect(t);

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Serial.print("TCA Port #"); Serial.println(t);

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for (uint8_t addr = 0; addr<=127; addr++) {

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if (addr == TCAADDR) continue;

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Wire.beginTransmission(addr);

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if (!Wire.endTransmission()) {

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Serial.print("Found I2C 0x"); Serial.println(addr,HEX);

}

}

}

Serial.println("\ndone");

}

void loop()

{

}

== SAA1064T data for driving center IO LED stack ==

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Center IO stack is a stack of 23 LED's, 22 blue and 1 green for ethernet activity. These are duplicated next to each other and driven by each their SAA1064T chips. Earlier we found the i2c address and just by playing around figured out that 4 segments of 1 byte binary values are used to set ship register.

void fillColumns() {

Serial.println("filling columns");

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Wire.beginTransmission(saa1064);

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Wire.write(1);

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Wire.write(0x7F); // 127 - 1111111

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Wire.write(0x7F); // 127 - 1111111

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Wire.write(0x7F); // 127 - 1111111

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Wire.write(0x1F); // 31 - 11111

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Wire.endTransmission();

colsFilled = 1;

}

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Here the last byte we send only is 5 bits since we only have 5 LEDs instead of 6 to address (total of 23). Also note that we start the transmission with a single bit.

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== Pinouts voltages from MLB ==

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* PWR fail LED - 0.00 V

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* UID LED - 4.5V

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