diff options
Diffstat (limited to 'src/mess/machine/coco.c')
-rw-r--r-- | src/mess/machine/coco.c | 18 |
1 files changed, 10 insertions, 8 deletions
diff --git a/src/mess/machine/coco.c b/src/mess/machine/coco.c index 2cedfd7b43c..d701d4f8baf 100644 --- a/src/mess/machine/coco.c +++ b/src/mess/machine/coco.c @@ -681,21 +681,23 @@ void coco_state::update_sound(void) /* determine the sound mux status */ soundmux_status_t status = soundmux_status(); + /* the SC77526 DAC chip internally biases the AC-coupled sound inputs for Cassette and Cartridge at the midpoint of the 3.9v output range */ + bool bCassSoundEnable = (status == (SOUNDMUX_ENABLE | SOUNDMUX_SEL1)); + bool bCartSoundEnable = (status == (SOUNDMUX_ENABLE | SOUNDMUX_SEL2)); + UINT8 cassette_sound = (bCassSoundEnable ? 0x40 : 0); + UINT8 cart_sound = (bCartSoundEnable ? 0x40 : 0); + /* determine the value to send to the DAC */ m_dac_output = (m_pia_1->a_output() & 0xFC) >> 2; - UINT8 sound_output = single_bit_sound + (status == SOUNDMUX_ENABLE ? m_dac_output << 1 : 0); - m_dac->write_unsigned8(sound_output); + UINT8 dac_sound = (status == SOUNDMUX_ENABLE ? m_dac_output << 1 : 0); + m_dac->write_unsigned8(single_bit_sound + dac_sound + cassette_sound + cart_sound); /* determine the cassette sound status */ - cassette_state cas_sound = (status == (SOUNDMUX_ENABLE | SOUNDMUX_SEL1)) - ? CASSETTE_SPEAKER_ENABLED - : CASSETTE_SPEAKER_MUTED; + cassette_state cas_sound = bCassSoundEnable ? CASSETTE_SPEAKER_ENABLED : CASSETTE_SPEAKER_MUTED; m_cassette->change_state(cas_sound, CASSETTE_MASK_SPEAKER); /* determine the cartridge sound status */ - m_cococart->cart_set_line( - COCOCART_LINE_SOUND_ENABLE, - (status == (SOUNDMUX_ENABLE | SOUNDMUX_SEL2)) ? COCOCART_LINE_VALUE_ASSERT : COCOCART_LINE_VALUE_CLEAR); + m_cococart->cart_set_line(COCOCART_LINE_SOUND_ENABLE, bCartSoundEnable ? COCOCART_LINE_VALUE_ASSERT : COCOCART_LINE_VALUE_CLEAR); } |