Original Interface Hardware

This is the original interface design, as conceived by Martin Mather in 2006.

A schematic of the original hardware can be found here: http://swhs.home.xs4all.nl/bbc/mmbeeb/

The original hardware uses the following BBC User Port connections:

User Port     SD Card
 (Master)     (Slave)
=========     =======
  CB1/PB1 ==> S_CLK  (Clock)
      CB2 <== S_MISO (Dout)
      PB0 ==> S_MOSI (Din)
       0V ==> S_SEL  (Select)

With this hardware, the 6522 shift register mode 2 can be used to provide high speed reads ("turbo reads"). This feature was introduced in MMFS 1.13.

TurboMMC Interface Hardware

A schematic of the TurboMMC hardware can be found here: http://stardot.org.uk/forums/viewtopic.php?t=9445&f=3#p110691

The TurboMMC hardware is a more complicated, as it uses PB[4:2] to control three buffers, providing two different operating modes.

When PB[4:2] are 010, then the hardware is configured as above, and the interface is compatible with the original hardware.

When PB[4:2] are 101, then the hardware is re-configured as:

User Port     SD Card
 (Master)     (Slave)
=========     =======
  CB1/PB1 ==> S_CLK  (Clock)
      n/c <== S_MISO (Dout)
      CB2 ==> S_MOSI (Din)
       0V ==> S_SEL  (Select)

With this hardware, the 6522 shift register modes 2 and 6 can be used to provide high speed reads ("turbo reads") and high speed writes ("turbo writes") respectively. This feature was introduced in MMFS 1.15.