mirror of
https://github.com/TomNisbet/TommyPROM.git
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103 lines
3.1 KiB
C++
103 lines
3.1 KiB
C++
// This controls the shift register that generates the address lines for A0..A15 for most
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// chip families.
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//
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// Note that this uses direct port control instead of digitalWrite calls so that the code
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// can run fast enough to meet the tBLC requirements for SDP and block writes. This
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// sacrifices portability and readability for speed.
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//
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// This code will only work on Arduino Uno and Nano hardware. The ports for other
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// Arduinos map to different IO pins.
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#include "PromAddressDriver.h"
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#define ADDR_CLK_HI A3
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#define ADDR_CLK_LO A4
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#define ADDR_DATA A5
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// Define masks for the address clk and data lines on PC3..PC5 for direct port control.
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#define ADDR_CLK_HI_MASK 0x08
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#define ADDR_CLK_LO_MASK 0x10
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#define ADDR_DATA_MASK 0x20
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// When using the 74LS595 shift registers, the RCLK lines of both shift registers can be
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// connected to D13 (PB5).
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#define RCLK_595_MASK 0x20
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void PromAddressDriver::begin()
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{
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// The address control pins are always outputs.
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pinMode(ADDR_DATA, OUTPUT);
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pinMode(ADDR_CLK_LO, OUTPUT);
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pinMode(ADDR_CLK_HI, OUTPUT);
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digitalWrite(ADDR_DATA, LOW);
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digitalWrite(ADDR_CLK_LO, LOW);
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digitalWrite(ADDR_CLK_HI, LOW);
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DDRB |= RCLK_595_MASK; // Set D13 as output
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// To save time, the setAddress only writes the hi byte if it has changed.
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// The value used to detect the change is initialized to a non-zero value,
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// so set an initial address to avoid the the case where the first address
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// written is the 'magic' initial address.
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setAddress(0x0000);
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}
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// Set a 16 bit address in the two address shift registers.
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void PromAddressDriver::setAddress(word address)
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{
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static byte lastHi = 0xca;
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byte hi = address >> 8;
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byte lo = address & 0xff;
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if (hi != lastHi)
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{
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setAddressRegister(ADDR_CLK_HI, hi);
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lastHi = hi;
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}
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setAddressRegister(ADDR_CLK_LO, lo);
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}
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// Shift an 8-bit value into one of the address shift registers. Note that
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// the data pins are tied together, selecting the high or low address register
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// is a matter of using the correct clock pin to shift the data in.
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void PromAddressDriver::setAddressRegister(uint8_t clkPin, byte addr)
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{
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byte mask = 0;
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if (clkPin == ADDR_CLK_HI)
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mask = ADDR_CLK_HI_MASK;
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else if (clkPin == ADDR_CLK_LO)
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mask = ADDR_CLK_LO_MASK;
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// Make sure the clock is low to start.
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PORTC &= ~mask;
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// Shift 8 bits in, starting with the MSB.
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for (int ix = 0; (ix < 8); ix++)
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{
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// Set the data bit
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if (addr & 0x80)
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{
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PORTC |= ADDR_DATA_MASK;
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}
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else
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{
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PORTC &= ~ADDR_DATA_MASK;
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}
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// Toggle the clock high then low
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PORTC |= mask;
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delayMicroseconds(3);
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PORTC &= ~mask;
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addr <<= 1;
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}
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// Toggle the output latch for 74LS595 hardware. For the default TommyPROM hardware
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// this just harmlessly writes to the D13 line that isn't connected to anything.
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PORTB &= ~RCLK_595_MASK;
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delayMicroseconds(1);
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PORTB |= RCLK_595_MASK;
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delayMicroseconds(1);
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PORTB &= ~RCLK_595_MASK;
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}
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