/// <summary>
/// Writes a byte of data to a specified port address
/// </summary>
/// <param name="port"></param>
/// <param name="value"></param>
public override void WritePort(ushort port, byte value)
{
// process IO contention
ContendPortAddress(port);
// get a BitArray of the port
BitArray portBits = new BitArray(BitConverter.GetBytes(port));
// get a BitArray of the value byte
BitArray bits = new BitArray(new byte[] { value });
// Check whether the low bit is reset
bool lowBitReset = !portBits[0]; // (port & 0x01) == 0;
AYDevice.WritePort(port, value);
UPDDiskDevice.WritePort(port, value);
// port 0x7ffd - hardware should only respond when bits 1 & 15 are reset and bit 14 is set
if (port == 0x7ffd)
{
if (!PagingDisabled)
{
// bits 0, 1, 2 select the RAM page
var rp = value & 0x07;
if (rp < 8)
{
RAMPaged = rp;
}
// bit 3 controls shadow screen
SHADOWPaged = bits[3];
// Bit 5 set signifies that paging is disabled until next reboot
PagingDisabled = bits[5];
// portbit 4 is the LOW BIT of the ROM selection
ROMlow = bits[4];
}
}
// port 0x1ffd - hardware should only respond when bits 1, 13, 14 & 15 are reset and bit 12 is set
if (port == 0x1ffd)
{
if (!PagingDisabled)
{
if (!bits[0])
{
// special paging is not enabled - get the ROMpage high byte
ROMhigh = bits[2];
// set the special paging mode flag
SpecialPagingMode = false;
}
else
{
// special paging is enabled
// this is decided based on combinations of bits 1 & 2
// Config 0 = Bit1-0 Bit2-0
// Config 1 = Bit1-1 Bit2-0
// Config 2 = Bit1-0 Bit2-1
// Config 3 = Bit1-1 Bit2-1
BitArray confHalfNibble = new BitArray(2);
confHalfNibble[0] = bits[1];
confHalfNibble[1] = bits[2];
// set special paging configuration
PagingConfiguration = ZXSpectrum.GetIntFromBitArray(confHalfNibble);
// set the special paging mode flag
SpecialPagingMode = true;
}
}
// bit 4 is the printer port strobe
PrinterPortStrobe = bits[4];
}
// Only even addresses address the ULA
if (lowBitReset)
{
// store the last OUT byte
LastULAOutByte = value;
/*
* Bit 7 6 5 4 3 2 1 0
+-------------------------------+
| | | | E | M | Border |
+-------------------------------+
*/
// Border - LSB 3 bits hold the border colour
if (ULADevice.borderColour != (value & BORDER_BIT))
{
ULADevice.UpdateScreenBuffer(CurrentFrameCycle);
}
ULADevice.borderColour = value & BORDER_BIT;
// Buzzer
BuzzerDevice.ProcessPulseValue((value & EAR_BIT) != 0);
// Tape
TapeDevice.WritePort(port, value);
// Tape
//TapeDevice.ProcessMicBit((value & MIC_BIT) != 0);
}
LastULAOutByte = value;
}
/// <summary>
/// Writes a byte of data to a specified port address
/// </summary>
public override void WritePort(ushort port, byte value)
{
// get a BitArray of the port
BitArray portBits = new BitArray(BitConverter.GetBytes(port));
// get a BitArray of the value byte
BitArray bits = new BitArray(new byte[] { value });
// handle AY port writes
AYDevice.WritePort(port, value);
// memory paging
// this is controlled by writes to port 0x7ffd
// but it is only partially decoded so it actually responds to any port with bits 1 and 15 reset
if (portBits[1] == false && portBits[15] == false)
{
Last7ffd = value;
// if paging is disabled then all writes to this port are ignored until the next reboot
if (!PagingDisabled)
{
// Bits 0, 1, 2 select the RAM page
var rp = value & 0x07;
if (RAMPaged != rp && rp < 8)
{
RAMPaged = rp;
}
// bit 3 controls shadow screen
if (SHADOWPaged != bits[3])
{
SHADOWPaged = bits[3];
}
// ROM page
if (bits[4])
{
// 48k basic rom
ROMPaged = 1;
}
else
{
// 128k editor and menu system
ROMPaged = 0;
}
// Bit 5 set signifies that paging is disabled until next reboot
PagingDisabled = bits[5];
}
else
{
// no changes to paging
}
}
if (port == 0x1ffd)
{
}
// Check whether the low bit is reset
// Technically the ULA should respond to every even I/O address
bool lowBitReset = !portBits[0]; // (port & 0x01) == 0;
// Only even addresses address the ULA
if (lowBitReset)
{
LastFe = value;
// store the last OUT byte
LastULAOutByte = value;
/*
* Bit 7 6 5 4 3 2 1 0
+-------------------------------+
| | | | E | M | Border |
+-------------------------------+
*/
// Border - LSB 3 bits hold the border colour
if (ULADevice.BorderColor != (value & BORDER_BIT))
{
//ULADevice.RenderScreen((int)CurrentFrameCycle);
ULADevice.BorderColor = value & BORDER_BIT;
}
// Buzzer
BuzzerDevice.ProcessPulseValue((value & EAR_BIT) != 0, _renderSound);
TapeDevice.WritePort(port, value);
// Tape
//TapeDevice.ProcessMicBit((value & MIC_BIT) != 0);
}
}
