Utility sketch to disable SDP on Ben Eater hardware

unlock-ben-eater-hardware/README.md

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+Utility to unlock 28C256 Software Data Protection (SDP) for the
+[Ben Eater EEPROM](https://github.com/beneater/eeprom-programmer)
+programmer design.  This hardware is similar to the TommyPROM hardware, but it uses
+different shift register chips and different pin assignments.
+
+To meet the timing requirements of the SDP unlock, this code uses direct port writes
+to set and read values on the data bus.  It will work Arduino Uno and Nano hardware,
+but would require changes for other platforms.

unlock-ben-eater-hardware/unlock-ben-eater-hardware.ino

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+// Utility to unlock 28C256 Software Data Protection (SDP) for the Ben Eater EEPROM
+// programmer design.  This hardware is similar to the TommyPROM hardware, but it uses
+// different shift register chips and different pin assignments.
+//
+// To meet the timing requirements of the SDP unlock, this code uses direct port writes
+// to set and read values on the data bus.  It will work Arduino Uno and Nano hardware,
+// but would require changes for other platforms.
+#define SHIFT_DATA 2
+#define SHIFT_CLK 3
+#define SHIFT_LATCH 4
+#define WRITE_EN 13
+
+
+// 32 byte test pattern to verify the EEPROM device.  The pattern includes a walking one
+// and a walking zero, which may help to detect pins that are tied together or swapped.
+byte data[] = {
+    'A',  'B',  'C',  'D',  'E',  'F',  'G',  'H',
+    0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80,
+    0x7f, 0xbf, 0xdf, 0xef, 0xf7, 0xfb, 0xfd, 0xfe,
+    0x00, 0xff, 0x55, 0xaa, '0',  '1',  '2',  '3'
+};
+
+void enableWrite()      { digitalWrite(WRITE_EN, LOW);}
+void disableWrite()     { digitalWrite(WRITE_EN, HIGH);}
+
+void setup() {
+    // put your setup code here, to run once:
+    pinMode(SHIFT_DATA, OUTPUT);
+    pinMode(SHIFT_CLK, OUTPUT);
+    pinMode(SHIFT_LATCH, OUTPUT);
+    disableWrite();
+    pinMode(WRITE_EN, OUTPUT);
+    Serial.begin(57600);
+
+    Serial.print("\nDisabling EEPROM Software Data Protection(SDP)...");
+    disableSoftwareWriteProtect();
+    Serial.println(" done\n");
+
+    // Program a test pattern and fill the remainder of the first block with 0xff
+    Serial.print("Programming EEPROM...");
+    for (word address = 0; (address < sizeof(data)); address++) {
+        writeEEPROM(address, data[address]);
+    }
+    for (word address = sizeof(data); (address < 256); address++) {
+        writeEEPROM(address, 0xff);
+    }
+    Serial.println(" done\n");
+
+    // Read and print out the contents of the EERPROM
+    Serial.println("Reading EEPROM");
+    printContents();
+}
+
+void loop() {
+}
+
+
+// Output the address bits and outputEnable signal using shift registers.
+void setAddress(int address, bool outputEnable) {
+    // Shift the address bits in
+    shiftOut(SHIFT_DATA, SHIFT_CLK, MSBFIRST, (address >> 8) | (outputEnable ? 0x00 : 0x80));
+    shiftOut(SHIFT_DATA, SHIFT_CLK, MSBFIRST, address);
+
+    // Latch the shift register contents into the output register.
+    digitalWrite(SHIFT_LATCH, LOW);
+    digitalWrite(SHIFT_LATCH, HIGH);
+    digitalWrite(SHIFT_LATCH, LOW);
+}
+
+// Read a byte from the EEPROM at the specified address.
+byte readEEPROM(int address) {
+    setDataBusMode(INPUT);
+    setAddress(address, /*outputEnable*/ true);
+    return readDataBus();
+}
+
+// Write a byte to the EEPROM at the specified address.
+void writeEEPROM(int address, byte data) {
+    setAddress(address, /*outputEnable*/ false);
+    setDataBusMode(OUTPUT);
+    writeDataBus(data);
+    enableWrite();
+    delayMicroseconds(1);
+    disableWrite();
+    delay(10);
+}
+
+// Read the first 256 byte block of the EEPROM and dump it to the serial monitor.
+void printContents() {
+    for (int base = 0; (base < 256); base += 16) {
+        byte data[16];
+        for (int offset = 0; offset <= 15; offset += 1) {
+            data[offset] = readEEPROM(base + offset);
+        }
+
+        char buf[80];
+        sprintf(buf, "%04x:  %02x %02x %02x %02x %02x %02x %02x %02x   %02x %02x %02x %02x %02x %02x %02x %02x",
+            base, data[0], data[1], data[2], data[3], data[4], data[5], data[6], data[7],
+            data[8], data[9], data[10], data[11], data[12], data[13], data[14], data[15]);
+        Serial.println(buf);
+    }
+}
+
+// Write the special six-byte code to turn off Software Data Protection.
+void disableSoftwareWriteProtect() {
+    disableWrite();
+    setDataBusMode(OUTPUT);
+
+    setByte(0xaa, 0x5555);
+    setByte(0x55, 0x2aaa);
+    setByte(0x80, 0x5555);
+    setByte(0xaa, 0x5555);
+    setByte(0x55, 0x2aaa);
+    setByte(0x20, 0x5555);
+
+    setDataBusMode(INPUT);
+    delay(10);
+}
+
+// Write the special three-byte code to turn on Software Data Protection.
+void enableSoftwareWriteProtect() {
+    disableWrite();
+    setDataBusMode(OUTPUT);
+
+    setByte(0xaa, 0x5555);
+    setByte(0x55, 0x2aaa);
+    setByte(0xa0, 0x5555);
+
+    setDataBusMode(INPUT);
+    delay(10);
+}
+
+// Set the I/O state of the data bus.
+// The 8 bits data bus are is on pins D5..D12.
+void setDataBusMode(uint8_t mode) {
+    // On the Uno and Nano, D5..D12 maps to the upper 3 bits of port D and the
+    // lower 5 bits of port B.
+    if (mode == OUTPUT) {
+        DDRB |= 0x1f;
+        DDRD |= 0xe0;
+    } else {
+        DDRB &= 0xe0;
+        DDRD &= 0x1f;
+    }
+}
+
+// Read a byte from the data bus.  The caller must set the bus to input_mode
+// before calling this or no useful data will be returned.
+byte readDataBus() {
+    return (PINB << 3) | (PIND >> 5);
+}
+
+// Write a byte to the data bus.  The caller must set the bus to output_mode
+// before calling this or no data will be written.
+void writeDataBus(byte data) {
+     PORTB = (PORTB & 0xe0) | (data >> 3);
+     PORTD = (PORTD & 0x1f) | (data << 5);
+}
+
+// Set an address and data value and toggle the write control.  This is used
+// to write control sequences, like the software write protect.  This is not a
+// complete byte write function because it does not set the chip enable or the
+// mode of the data bus.
+void setByte(byte value, word address) {
+    setAddress(address, false);
+    writeDataBus(value);
+
+    delayMicroseconds(1);
+    enableWrite();
+    delayMicroseconds(1);
+    disableWrite();
+}