From a929b15424546e929769e028f12b8c99b237ec34 Mon Sep 17 00:00:00 2001 From: couriersud Date: Sun, 21 Jun 2015 21:04:16 +0200 Subject: [PATCH] Left a comment in AY8910.c about io ports A and B. (nw) The io ports are designed as open collector outputs. Bits 7 and 8 of AY_ENABLE only enable (low) or disable (high) the pull up resistors. The YM2149 datasheet specifies those pull up resistors as 60k to 600k (min / max). We do need a callback for those two flags. Kid Niki (Irem m62) is one such case were it makes a difference in comparison to a standard TTL output. --- src/emu/sound/ay8910.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/src/emu/sound/ay8910.c b/src/emu/sound/ay8910.c index 9decdb85c08..9e8d397ff7a 100644 --- a/src/emu/sound/ay8910.c +++ b/src/emu/sound/ay8910.c @@ -1004,6 +1004,12 @@ int ay8910_device::ay8910_read_ym() /* even if the port is set as output, we still need to return the external data. Some games, like kidniki, need this to work. + + FIXME: The io ports are designed as open collector outputs. Bits 7 and 8 of AY_ENABLE + only enable (low) or disable (high) the pull up resistors. The YM2149 datasheet + specifies those pull up resistors as 60k to 600k (min / max). + We do need a callback for those two flags. Kid Niki (Irem m62) is one such + case were it makes a difference in comparison to a standard TTL output. */ if (!m_port_a_read_cb.isnull()) m_regs[AY_PORTA] = m_port_a_read_cb(0);