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 firstname.lastname@example.org www.jbrain.com Message was sent through the cbm-hackers mailing listReceived on 2012-02-13 04:00:03
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