From 0a1cbc1924be60c11534cfd57509b75283624b9c Mon Sep 17 00:00:00 2001 From: Thomas Harte Date: Fri, 15 Jun 2018 15:45:34 -0400 Subject: [PATCH] First version; what I currently believe about the Mockingboard based on a schematic. --- The-Mockingboard.md | 29 +++++++++++++++++++++++++++++ 1 file changed, 29 insertions(+) create mode 100644 The-Mockingboard.md diff --git a/The-Mockingboard.md b/The-Mockingboard.md new file mode 100644 index 0000000..780f4ba --- /dev/null +++ b/The-Mockingboard.md @@ -0,0 +1,29 @@ +The Mockingboards are a series of audio expansions for the Apple II, the most common of which provides stereo sound from a combination of two 6522s, connected to two AY-3-8910s. + +== AY-3-8910s == +Each AY is connected to its 6522: +* the 6522 port A connected to the AY's data pins; +* bit 0 of the 6522's port B connected to the AY's BC1; +* bit 1 of the 6522's port B connected to the AY's BCDIR; +* BC2 connected to +5v; and +* bit 2 of the 6522's port B connected to the AY's reset. + +The three channels from each AY are mixed together with equal volume. + +== 6522s == +The 6522s are exposed to the processor's bus: +* the four register select lines are connected to address lines 0 to 3; and +* the reset and data lines connected as expected. + +The 6522 for the left channel: +* is selected when address line 7 is low; and +* its interrupt output is connected to the processor's IRQ input. + +The 6522 for the right channel: +* is selected when address line 7 is high; and +* its interrupt output is connected to the processor's NMI input. + +Both also require the board's IOSEL to be active — they appear only in the ordinary IO area for their board. + +== Clock Rate == +Both the 6522s and the AYs are clocked according to the Apple card's phase 1 clock input. So they are clocked at the same rate as the CPU. \ No newline at end of file