TomNisbet · Ghostboo124 · Nov 9, 2025 · Nov 9, 2025 · Nov 9, 2025 · Dec 3, 2025
diff --git a/TommyPROM/Configure.h b/TommyPROM/Configure.h
@@ -1,7 +1,9 @@
 // Uncomment this to enable extra debugging commands and code
 
-//#define ENABLE_DEBUG_COMMANDS
+// #define ENABLE_DEBUG_COMMANDS
 
+// Uncomment this to enable compilation for the Arduino Mega
+// #define IS_MEGA
 
 // Uncomment ONLY ONE of these to choose the PROM device code that will be
 // compiled in.

diff --git a/TommyPROM/PromAddressDriver.cpp b/TommyPROM/PromAddressDriver.cpp
@@ -7,9 +7,13 @@
 //
 // This code will only work on Arduino Uno and Nano hardware.  The ports for other
 // Arduinos map to different IO pins.
+//
+// Ghostboo124: Arduino Mega hardware support has been added.
 
 #include "PromAddressDriver.h"
 
+#ifndef IS_MEGA // if this isn't an arduino mega
+
 #define ADDR_CLK_HI     A3
 #define ADDR_CLK_LO     A4
 #define ADDR_DATA       A5
@@ -120,3 +124,92 @@ void PromAddressDriver::setAddressRegister(uint8_t clkPin, byte addr)
     delayMicroseconds(1);
     PORTB &= ~RCLK_595_MASK;
 }
+
+#else // #ifndef IS_MEGA
+
+// Address lines A0..A18 are controlled by D22..D40.
+#define ADDR_MASK_A 0xff // D22..D29 = PA0..PA7 = A0..A7
+#define ADDR_MASK_C 0xff // D30..D37 = PC7..PC0 = A8..A15
+#define ADDR_MASK_D 0x80 // D38      = PD7      = A16
+#define ADDR_MASK_G 0x06 // D39..D40 = PG2..PG1 = A17..A18
+
+void PromAddressDriver::begin()
+{
+    // The address control pins are always outputs.
+    DDRA |= ADDR_MASK_A; // Set D22..D29 as outputs
+    DDRC |= ADDR_MASK_C; // Set D30..D37 as outputs
+    DDRD |= ADDR_MASK_D; // Set D38 as output
+    DDRG |= ADDR_MASK_G; // Set D39..D40 as outputs
+
+    // To save time, the setAddress only writes the hi byte if it has changed.
+    // The value used to detect the change is initialized to a non-zero value,
+    // so set an initial address to avoid the the case where the first address
+    // written is the 'magic' initial address.
+    setAddress(0x0000);
+}
+
+// Set the address pins to a given address.
+void PromAddressDriver::setAddress(uint32_t address)
+{
+    static byte lastHi = 0xca;
+    static byte lastUpper = 0xca;
+    byte upper = (address >> 16) & 0xff;
+    byte hi = (address >> 8) & 0xff;
+    byte lo = address & 0xff;
+
+    if (upper != lastUpper)
+    {
+        setUpperAddress(upper);
+        lastUpper = upper;
+    }
+    if (hi != lastHi)
+    {
+        setLowerAddress(hi, true);
+        lastHi = hi;
+    }
+    setLowerAddress(lo, false);
+}
+
+// Set the upper address bits on the address pins.
+void PromAddressDriver::setUpperAddress(byte addr)
+{
+    // Set the upper address on pins D38..D40.
+
+    // D38
+    if (addr & 0x01)
+        PORTD |= ADDR_MASK_D;
+    else
+        PORTD &= ~ADDR_MASK_D;
+
+    // D39, D40
+    uint8_t portG = PORTG & ~ADDR_MASK_G;
+    if (addr & 0x02)        // A17 -> PG2
+        portG |= 0x04;
+    if (addr & 0x04)        // A18 -> PG1
+        portG |= 0x02;
+    PORTG = portG;
+}
+
+
+// Write the 8-bit low or high address values to the address pins.
+void PromAddressDriver::setLowerAddress(byte addr, bool isHigh)
+{
+    if (isHigh) { // If we are working with A8..A15
+        // D30..D37 = PC7..PC0 = A8..A15
+        uint8_t portC = 0;
+        if (addr & 0x01) portC |= 0x80; // A8 -> PC7 (D30)
+        if (addr & 0x02) portC |= 0x40; // A9 -> PC6 (D31)
+        if (addr & 0x04) portC |= 0x20; // A10 -> PC5 (D32)
+        if (addr & 0x08) portC |= 0x10; // A11 -> PC4 (D33)
+        if (addr & 0x10) portC |= 0x08; // A12 -> PC3 (D34)
+        if (addr & 0x20) portC |= 0x04; // A13 -> PC2 (D35)
+        if (addr & 0x40) portC |= 0x02; // A14 -> PC1 (D36)
+        if (addr & 0x80) portC |= 0x01; // A15 -> PC0 (D37)
+        PORTC = portC;
+    } else { // If we are working with A0..A7
+        // D22..D29 = PA0..PA7 = A0..A7
+        PORTA = addr;
+    }
+}
+
+#endif // #ifndef IS_MEGA
diff --git a/TommyPROM/PromAddressDriver.h b/TommyPROM/PromAddressDriver.h
@@ -2,15 +2,19 @@
 #define INCLUDE_PROM_ADDRESS_DRIVER_H
 
 #include "Arduino.h"
+#include "Configure.h"
 
 class PromAddressDriver {
   public:
     static void begin();
     static void setAddress(uint32_t address);
-
   private:
     static void setUpperAddress(byte addr);
+#ifndef IS_MEGA
     static void setAddressRegister(uint8_t clkPin, byte addr);
+#else // #ifndef IS_MEGA
+    static void setLowerAddress(byte addr, bool isHigh);
+#endif // #ifndef IS_MEGA
 };
 
 

diff --git a/TommyPROM/PromDevice.cpp b/TommyPROM/PromDevice.cpp
@@ -103,6 +103,7 @@ void PromDevice::printDebugStats() {
 // on pins D2..D9.
 void PromDevice::setDataBusMode(uint8_t mode)
 {
+#ifndef IS_MEGA
     // On the Uno and Nano, D2..D9 maps to the upper 6 bits of port D and the
     // lower 2 bits of port B.
     if (mode == OUTPUT)
@@ -117,21 +118,71 @@ void PromDevice::setDataBusMode(uint8_t mode)
         PORTB |= 0x03;  // set pullup resistors
         PORTD |= 0xfc;
     }
+#else // #ifndef IS_MEGA
+    // On the Mega, D2..D9 maps to stupid random ports...
+    if (mode == OUTPUT) {
+        DDRE |= 0x38; // D2,D3,D5 = PE4, PE5, PE3
+        DDRG |= 0x20; // D4 = PG5
+        DDRH |= 0x78; // D6..D9 = PH3..PH6
+    } else {
+        // Set to input
+        DDRE &= ~0x38;
+        DDRG &= ~0x20;
+        DDRH &= ~0x78;
+        // set pullup resistors
+        PORTE |= 0x38;
+        PORTG |= 0x20;
+        PORTH |= 0x78;
+    }
+
+#endif // #ifndef IS_MEGA
 }
 
 
 // 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 PromDevice::readDataBus()
 {
+#ifndef IS_MEGA
     return (PINB << 6) | (PIND >> 2);
+#else // #ifndef IS_MEGA
+    byte data = 0;
+    if (PINE & 0x10) data |= 0x01;    // D2 = PE4
+    if (PINE & 0x20) data |= 0x02;    // D3 = PE5
+    if (PING & 0x20) data |= 0x04;    // D4 = PG5
+    if (PINE & 0x08) data |= 0x08;    // D5 = PE3
+    if (PINH & 0x08) data |= 0x10;    // D6 = PH3
+    if (PINH & 0x10) data |= 0x20;    // D7 = PH4
+    if (PINH & 0x20) data |= 0x40;    // D8 = PH5
+    if (PINH & 0x40) data |= 0x80;    // D9 = PH6
+    return data;
+#endif // #ifndef IS_MEGA
 }
 
 
 // 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 PromDevice::writeDataBus(byte data)
 {
+#ifndef IS_MEGA
      PORTB = (PORTB & 0xfc) | (data >> 6);
      PORTD = (PORTD & 0x03) | (data << 2);
+#else // #ifndef IS_MEGA
+    uint8_t portE = PORTE & ~0x38; // clear PE3,4,5
+    if (data & 0x01) portE |= 0x10; // bit0 -> PE4 (D2)
+    if (data & 0x02) portE |= 0x20; // bit1 -> PE5 (D3)
+    if (data & 0x08) portE |= 0x08; // bit3 -> PE3 (D5)
+    PORTE = portE;
+
+    uint8_t portG = PORTG & ~0x20; // clear PG5
+    if (data & 0x04) portG |= 0x20; // bit2 -> PG5 (D4)
+    PORTG = portG;
+
+    uint8_t portH = PORTH & ~0x78; // clear PH3..PH6
+    if (data & 0x10) portH |= 0x08; // bit4 -> PH3 (D6)
+    if (data & 0x20) portH |= 0x10; // bit5 -> PH4 (D7)
+    if (data & 0x40) portH |= 0x20; // bit6 -> PH5 (D8)
+    if (data & 0x80) portH |= 0x40; // bit7 -> PH6 (D9)
+    PORTH = portH;
+#endif // #ifndef IS_MEGA
 }
diff --git a/TommyPROM/PromDevice28C.cpp b/TommyPROM/PromDevice28C.cpp
@@ -32,12 +32,12 @@ void PromDevice28C::begin()
 
     // Define the EEPROM control pins as output, making sure they are all
     // in the disabled state.
-    digitalWrite(OE, HIGH);
     pinMode(OE, OUTPUT);
-    digitalWrite(CE, HIGH);
+    digitalWrite(OE, HIGH);
     pinMode(CE, OUTPUT);
-    digitalWrite(WE, HIGH);
+    digitalWrite(CE, HIGH);
     pinMode(WE, OUTPUT);
+    digitalWrite(WE, HIGH);
 
     // This chip uses the shift register hardware for addresses, so initialize that.
     PromAddressDriver::begin();

diff --git a/TommyPROM/TommyPROM.ino b/TommyPROM/TommyPROM.ino
@@ -18,10 +18,8 @@
 #include "CmdStatus.h"
 #include "XModem.h"
 
-
 static const char * MY_VERSION = "3.7";
 
-
 // Global status
 CmdStatus cmdStatus;
 

diff --git a/docs/_docs/00-intro.md b/docs/_docs/00-intro.md
@@ -66,7 +66,8 @@ use this version, just compile and upload it to the Arduino.
 that it can run quickly enough to meet 28C series chip timing requirements for SDP
 unlocking.  To use different Arduino hardware, like the Micro, the board-specific code in
 PromDevice.cpp and PromAddressDriver.cpp must be changed to match the port mappings
-between the ATmega chip and the Arduino I/O pins.
+between the ATmega chip and the Arduino I/O pins. If you are compiling for the
+Arduino Mega2560, uncomment the IS_MEGA line in Configure.
 
 Because the Arduino has limited code and RAM space available, only one PROM driver is
 compiled in at a time.  To change drivers, uncomment the desired PROM_IS_xx line in

diff --git a/docs/_docs/50-ops-500-troubleshooting.md b/docs/_docs/50-ops-500-troubleshooting.md
@@ -11,11 +11,11 @@ hardware allows access to individual control lines from the Arduino to verify th
 hardware was assembled correctly.
 
 The verifier sketch can be used without a chip installed to scope out address and data
-lines.  It also offers low-level control when the chip is installed.  
+lines.  It also offers low-level control when the chip is installed.
 
 THIS TOOL USES DIRECT PORT ACCESS ON THE ARDUINO.  CHECK TO MAKE SURE IT IS COMPATIBLE
-WITH YOUR BOARD BEFORE USING.  It will work correctly on the Uno, Nano, and Boarduino.  It
-WILL NOT WORK on the Micro.
+WITH YOUR BOARD BEFORE USING.  It will work correctly on the Uno, Nano, Boarduino, and
+Mega2560 with configuration changes.  It WILL NOT WORK on the Micro.
 
 Note that the commands write to the individual 28C control lines with some exceptions to
 protect the chip and the host Arduino:

diff --git a/docs/_docs/design-100-hardware.md b/docs/_docs/design-100-hardware.md
@@ -16,14 +16,20 @@ The basic circuit is as follows:
 * Pins A3..A5 control shift registers to produce the address lines.
 * Pins D10..D12 control A<sub>16</sub>..A<sub>18</sub> for chips larger than 64K bytes.
 
+If you use a Arduino Mega2560, the basic circuit is as follows:
+* Pins D2..D9 are wired to the data lines on teh target PROM.
+* Pins A0..A2 are wired to the WE, CE, and OE control lines of the target PROM.
+* Pins D22..D37 control the address lines A<sub>0</sub>..A<sub>15</sub>.
+* Pins D38..D40 control the address lines A<sub>16</sub>..A<sub>18</sub> for chips larger than 64K bytes
+
 Note that the existing design uses 74LS164 shift registers, but another 8-bit parallel out
 shift register, like the 74LS595, can be used instead with some pin changes.  See the
 [74LS595 Shift Registers](#74ls595-shift-registers) section below for details.
 
 The two shift registers can produce a sixteen bit address, although the 28C256 only needs
 15 addresses. Chips larger than 64K are supported by using the shift registers for
 A<sub>0</sub>..A<sub>15</sub> and connecting Arduino pins D10..D12 to the chip's
-A<sub>16</sub>..A<sub>18</sub>
+A<sub>16</sub>..A<sub>18</sub> or for the Mega2560, pins D38..D40 to A<sub>16</sub>..A<sub>18</sub>.
 
 [![TommyPROM Nano Schematic](images/TommyPROM-nano-sch.png)](images/TommyPROM-nano-sch.png)
 
@@ -59,7 +65,7 @@ larger chips like the 27C040.
 3. The D13 pin controls the output register on the '595 shift registers.  This pin is not
 connected when using the 74LS164.
 
-Note that the 74LS595s have two additional pins that need to be connected.  
+Note that the 74LS595s have two additional pins that need to be connected.
 * An output enable pin, labeled as either G or OE in the datasheet,  must be tied LOW for
 both chips or else they will not produce any signal on their output lines.
 * A reset pin, labeled as RESET or SRCLR, must be tied HIGH for both chips or else the

diff --git a/docs/_docs/design-200-software.md b/docs/_docs/design-200-software.md
@@ -41,7 +41,7 @@ To meet the timing requirements for block writes and 28C chip unlocking, the Pro
 class accesses the shift registers and data bus using direct port writes instead of 8
 individual pin accesses.  This greatly increases performance, but it makes the code
 dependent on the particular flavor of Arduino being used.  The code supports the Uno,
-Nano, and Boarduino versions of Arduino hardware or any other variant that uses that same
+Nano, Boarduino, and Mega2560 versions of Arduino hardware or any other variant that uses that same
 mapping of ATMega ports to I/O pins.  To support a different Arduino board, either change
 the pins used to match the mapping in the software, or change the hardware-specific code
 in PromDevice.cpp and PromAddressDriver.cpp.
@@ -79,5 +79,5 @@ the Vdd switching hardware that toggles the Vdd pin between the normal 5V value
 ### PromAddressDriver class
 
 Although not actually a subclass of PromDevice, this contains the code to drive the shift
-registers that provide the address lines. If this hardware is used, the PromDeviceXX class
+registers that provide the address lines or directly control the address lines on the Mega2560. If this hardware is used, the PromDeviceXX class
 can call this code to implement the SetAddress methods.
diff --git a/docs/_docs/design-400-extending.md b/docs/_docs/design-400-extending.md
@@ -26,7 +26,7 @@ already been used with these chips for read-only operations.
 
 The current design can directly address chips as large as 512K bytes, like the 29C040. Use
 the shift registers for A<sub>0</sub>..A<sub>15</sub> and wire Arduino pins D10..D12 to
-A<sub>16</sub>..A<sub>18</sub> on the target chip.
+A<sub>16</sub>..A<sub>18</sub> on the target chip or on the Mega2560, pins D38 to D40 to A<sub>16</sub>..A<sub>18</sub>.
 
 # Software
 

diff --git a/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_102812.zip b/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_102812.zip
diff --git a/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_121856.zip b/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_121856.zip
diff --git a/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_124125.zip b/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_124125.zip
diff --git a/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_132645.zip b/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_132645.zip
diff --git a/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_140109.zip b/...cs/TommyPROM-Mega2560/TommyPROM-Mega2560-backups/TommyPROM-Mega2560-2025-11-24_140109.zip
diff --git a/schematics/TommyPROM-Mega2560/TommyPROM-Mega2560.kicad_pcb b/schematics/TommyPROM-Mega2560/TommyPROM-Mega2560.kicad_pcb
@@ -0,0 +1,2 @@
+(kicad_pcb (version 20241229) (generator "pcbnew") (generator_version "9.0")
+)
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,2 @@
		(kicad_pcb (version 20241229) (generator "pcbnew") (generator_version "9.0")
		)