I found an original DMG gameboy with a broken screen. I would like to open it up and replace the buttons and fix the screen as well as possibly a few other mods. However, after removing 2 of the screws, I discovered that the other 4 screws were too stripped to get out with my screwdriver.

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Use a fingernail (or small coin) to push down on the battery door latch and remove the battery door. The release latch is a plastic spring clip. If your Game Boy is getting on in years, be careful as the plastic may be brittle.
The Game Boy can be imagined as a portable version of the NES with limited power, but you’ll see that it included very interesting new functionality. CPU The main processor is a Sharp LR35902, a mix between the Z80 and the Intel 8080 that runs at 4.19 MHz.

This documents the behavior of Game Boy sound; details which aren't relevant to the observable behavior have been omitted unless they clarify understanding. It is aimed at answering all questions about exact operation, rather than describing how to use sound effectively in Game Boy programs. Values in hexadecimal (base 16) are generally written with a $ prefix. Bits are numbered from 0 to 7, where bit N has a weight of 2^N. A nibble is 4 bits, half a byte. 2.2 linear and nonlinear relationsmr. macs page. Obscure behavior is described separately to increase clarity elsewhere.

The Game Boy has four sound channels: two square waves with adjustable duty, a programmable wave table, and a noise generator. Each has some kind of frequency (pitch) control. The first square channel also has an automatic frequency sweep unit to help with sound effects. The squares and noise each have a volume envelope unit to help with fading notes and sound effects, while the wave channel has only limited manual volume control. Each channel has a length counter that can silence the channel after a preset time, to handle note durations. Each channel can be individually panned to the far left, center, or far right. The master volume of the left and right outputs can also be adjusted.

Different versions of the Game Boy sound hardware have slightly different behavior. The following models have been tested:

DMG-CPU-03 original Game Boy
DMG-CPU-05
DMG-CPU-06
MGB-LCPU-01 Game Boy Pocket
CGB-CPU-02 Game Boy Color
CGB-CPU-04
CGB-CPU-05

Sound registers are mapped to $FF10-$FF3F in memory. Each channel has five logical registers, NRx0-NRx4, though some don't use NRx0. The value written to bits marked with '-' has no effect. Reference to the value in a register means the last value written to it.

Each channel has a frequency timer which clocks a waveform generator. The waveform's volume is adjusted and fed to the mixer. The mixer converts each channel's waveform into an electrical signal and outputs this to the left and/or right channels. Finally, a master volume control adjusts the left and right outputs. The channels have the following units that are connected from left to right:

The mixer has a separate DAC for each channel, followed by on/off controls for left and right outputs. The left/right outputs from each channel are then added together and fed to the left/right master volume controls.

In general, all units in the channels are always running. For example, even if a channel is silent, several units will still be calculating values even though they aren't used.

A timer generates an output clock every N input clocks, where N is the timer's period. If a timer's rate is given as a frequency, its period is 4194304/frequency in Hz. Each timer has an internal counter that is decremented on each input clock. When the counter becomes zero, it is reloaded with the period and an output clock is generated.

The frame sequencer generates low frequency clocks for the modulation units. It is clocked by a 512 Hz timer.

A length counter disables a channel when it decrements to zero. It contains an internal counter and enabled flag. Writing a byte to NRx1 loads the counter with 64-data (256-data for wave channel). The counter can be reloaded at any time.

A channel is said to be disabled when the internal enabled flag is clear. When a channel is disabled, its volume unit receives 0, otherwise its volume unit receives the output of the waveform generator. Other units besides the length counter can enable/disable the channel as well.

Each length counter is clocked at 256 Hz by the frame sequencer. When clocked while enabled by NRx4 and the counter is not zero, it is decremented. If it becomes zero, the channel is disabled.

A volume envelope has a volume counter and an internal timer clocked at 64 Hz by the frame sequencer. When the timer generates a clock and the envelope period is not zero, a new volume is calculated by adding or subtracting (as set by NRx2) one from the current volume. If this new volume within the 0 to 15 range, the volume is updated, otherwise it is left unchanged and no further automatic increments/decrements are made to the volume until the channel is triggered again.

When the waveform input is zero the envelope outputs zero, otherwise it outputs the current volume.

Writing to NRx2 causes obscure effects on the volume that differ on different Game Boy models (see obscure behavior).

A square channel's frequency timer period is set to (2048-frequency)*4. Four duty cycles are available, each waveform taking 8 frequency timer clocks to cycle through:

The first square channel has a frequency sweep unit, controlled by NR10. This has a timer, internal enabled flag, and frequency shadow register. It can periodically adjust square 1's frequency up or down.

During a trigger event, several things occur:

Square 1's frequency is copied to the shadow register.
The sweep timer is reloaded.
The internal enabled flag is set if either the sweep period or shift are non-zero, cleared otherwise.
If the sweep shift is non-zero, frequency calculation and the overflow check are performed immediately.

Frequency calculation consists of taking the value in the frequency shadow register, shifting it right by sweep shift, optionally negating the value, and summing this with the frequency shadow register to produce a new frequency. What is done with this new frequency depends on the context.

The overflow check simply calculates the new frequency and if this is greater than 2047, square 1 is disabled.

The sweep timer is clocked at 128 Hz by the frame sequencer. When it generates a clock and the sweep's internal enabled flag is set and the sweep period is not zero, a new frequency is calculated and the overflow check is performed. If the new frequency is 2047 or less and the sweep shift is not zero, this new frequency is written back to the shadow frequency and square 1's frequency in NR13 and NR14, then frequency calculation and overflow check are run AGAIN immediately using this new value, but this second new frequency is not written back.

Square 1's frequency can be modified via NR13 and NR14 while sweep is active, but the shadow frequency won't be affected so the next time the sweep updates the channel's frequency this modification will be lost.

The noise channel's frequency timer period is set by a base divisor shifted left some number of bits.

The linear feedback shift register (LFSR) generates a pseudo-random bit sequence. Alt finders for mac os xfluidrenew. It has a 15-bit shift register with feedback. When clocked by the frequency timer, the low two bits (0 and 1) are XORed, all bits are shifted right by one, and the result of the XOR is put into the now-empty high bit. If width mode is 1 (NR43), the XOR result is ALSO put into bit 6 AFTER the shift, resulting in a 7-bit LFSR. The waveform output is bit 0 of the LFSR, INVERTED.

The wave channel plays a 32-entry wave table made up of 4-bit samples. Each byte encodes two samples, the first in the high bits. The wave channel has a sample buffer and position counter.

The wave channel's frequency timer period is set to (2048-frequency)*2. When the timer generates a clock, the position counter is advanced one sample in the wave table, looping back to the beginning when it goes past the end, then a sample is read into the sample buffer from this NEW position.

The DAC receives the current value from t

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