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When using the MBHP_Genesis module with a MCU supplied at less than 5V, especially when using several modules in parallel, a buffer circuit will be required between the MCU and the modules. This is a very simple circuit that consists of two 20-pin 74HCT series ICs and two power supply bypass capacitors, and can easily be built on prototyping board.
For buffering the data lines, a bidirectional buffer must be used; a common one is 74HCT245. Connect the eight lines from the MCU board to data pins B; connect the eight lines from the MBHP_Genesis board to data pins A; connect the /OE pin to the buffered /CS line (on the MBHP_Genesis side of the buffer); connect the DIR pin to the buffered /RD line (same thing); and connect a 0.1uF capacitor across the supply rails of the buffer chip.
For buffering the address lines, which are unidirectional from MCU to MBHP_Genesis, use a 74HCT541, with its two /OE pins always active (grounded). Alternatively you can use another 74HCT245, with /OE permanently active (grounded) and DIR set appropriately to always send the signals from the MCU to the MBHP_Genesis board. Again, bypass the supply rails with a capacitor.
Both buffers must be powered from +5V, not +3.3V or whatever the MCU uses. In addition, the MCU must be tolerant of 5V signals being applied to its I/O pins (the CORE_STM32F4 module is tolerant)–otherwise it will damage the MCU!
|Qty||Ref. Deg.||Part Name||Mouser Part Number||Description / Notes|
|1||U101||74HCT245||595-SN74HCT245N||Bidirectional buffer chip|
|2||[U101], [U102]||20-pin 0.3“ DIP socket||571-1-2199298-6||Socket for chips|
|2||J101, J102||10×2 pin header, 0.1” pitch||649-68691-420HLF||Connectors to core and MBHP_Genesis module|
|1||J103||2×1 pin header, 0.1“ pitch||571-826936-2||Connector for +5V power from core|
|2||C101, C102||0.1 uF||21RZ310-RC||Power supply filtering capacitors for chips (place one next to each chip's +5V connection)|
|1||C103||10 uF||140-REA100M1HBK0511P||Power supply filtering capacitor for board|