Any thoughts? On 2/12/2012 9:53 PM, Jim Brain wrote: > On 2/11/2012 11:11 AM, Gerrit Heitsch wrote: >> On 02/11/2012 07:33 AM, Jim Brain wrote: >>> Anyone see issues with wiring up a I2C-based (DS1307-type) RTC to the >>> cassette port with SCK on WRITE and SDA (data) on sense? Looking at >>> schematics, READ is often hooked to CA1 or similar read-only pin, but >>> SENSE appears to be on a GPIO on all CBM machines I found. Obviously, >>> the RTC would not work if the buttons were pushed on the player, but >>> are >>> there other concerns? >> >> In case you built that setup, it would be worth thinking about >> including a space/socket for a 24Cxxx I2C-EEPROM. They are small >> (8pin DIP or 8pin SMD) but give you up to 256KByte (24C2048) memory. >> They only need +5V and GND besides the I2C connection so the only >> additional cost for quite a bit nonvolatile storage would be the PCB >> space. >> >> Gerrit >> >> >> Message was sent through the cbm-hackers mailing list > Updates: > > * I decided to try the MOTOR/WRITE idea, as some suggested > * I ditched the 2 resistor voltage divider on MOTOR in favor of an NPN > NOT setup. That should allow faster signal response. That resolved > one of my major concerns with using MOTOR. > * I checked, and 24CXXX I2C EEPROMs use the same pinout as the 1307 > RTC, so the same PCB will work for both. Since it's a pass-through > PCB, they can be chained. > * I mapped the EEPROM on the cassette side of the pinouts, so the SMD > jumpers can be cut and the uC could have total control of the > EEPROM. I thought that might allow a 256kB "tape" emulator, dunno. > > Still worried about accidentally writing to a tape since I'm using > MOTOR, but I guess the code can check sense before it starts and fail > if sense is active. (low). > > Here are the various options: > > v2: SCK on WRITE, SDA on SENSE (original posting) > http://www.go4retro.com/gallery/C2NPower/C2NPowerV2-Schematic > http://www.go4retro.com/gallery/C2NPower/C2NPowerV2-PCB > > v2a: SCK on MOTOR, SDA on WRITE, MOTOR fed through inverting NPN > setup. (Ruud et al suggestion) > http://www.go4retro.com/gallery/C2NPower/C2NPowerV2a-Schematic > http://www.go4retro.com/gallery/C2NPower/C2NPowerV2a-PCB > > v2b: Remapped some uC pins to Cassette port to allow for better routing > http://www.go4retro.com/gallery/C2NPower/C2NPowerV2b-Schematic > http://www.go4retro.com/gallery/C2NPower/C2NPowerV2b-PCB > > v2c: Moved RTC footprint closer to XTAL for RTC. Rerouted some of the > lines for better layout and less EMI > http://www.go4retro.com/gallery/C2NPower/C2NPowerV2c-Schematic > http://www.go4retro.com/gallery/C2NPower/C2NPowerV2c-PCB > > Disclaimer: Last minute changes, like enlarging PWR trace width and > MOTOR trace width, were only done on 2c, but would be done on any > production board. > > Thoughts? > > Jim > -- Jim Brain brain@jbrain.com www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2012-02-14 04:00:03
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