--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bb2fc/README	Mon Oct 21 00:53:38 2019 +0000
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+The little board to be built in this project is an adapter for connecting an
+OMAP BeagleBoard-xM to a FreeCalypso device, specifically connecting Calypso's
+MCSI to OMAP's McBSP (primary objective) and also connecting a 4-wire UART
+(data + hw flow control) between the two devices - BB expansion interface
+provides such a UART, and it costs us very little extra effort to connect it
+along with MCSI.
+
+The present adapter will plug into the expansion header on the bottom side of
+the BeagleBoard, implement logic voltage level translation between OMAP's 1.8 V
+and Calypso's 2.8 V using the 1.8 V and 5 V power supplies provided by the
+BeagleBoard, and bring 2.8 V UART and MCSI interfaces out on headers, intended
+to be connected to a FreeCalypso board with jumper wires.
+
+The logic voltage level translation function will be accomplished using two
+74AVC4T774PW ICs, one for the UART and one for MCSI.  As a somewhat arbitrary
+pick made for greater ease of PCB layout, the A side of each translating
+transceiver IC will be the 2.8 V side and the B side will be the 1.8 V side.
+Each of the 4 1-bit channels in the 74AVC4T774PW has its own direction control
+pin, allowing us to neatly use one of these ICs for each 4-wire interface
+despite mixed signal directions.  MCSI_CLK and MCSI_FSYNCH are assumed to be
+outputs from the Calypso like they are when driven by the DSP ROM code in the
+silicon, and they will be voltage-translated in the Calypso to OMAP direction;
+the other direction is NOT supported.