1
Discussion - Hardware / Re: ft245 (232 or 2232 in 245 mode) interface to 68000 bus?
« on: December 25, 2019, 09:42:41 PM »Quote
I don't know about DMA, but lowendmac.com says the Plus could do about 250kbytes/sec, which seems pretty darned good to me, actually. Getting 1Mbyte/sec with just an 8MHz 68k plus an FT245 is going to be really difficult, I fear. The minimum bus cycle on the 68k is 4 clocks, and you'll be burning a few of those just to fetch your write instruction. So that 8MHz divides down really fast. Especially if you're wanting to do more than just spam the FT245--which seems a foregone conclusion.
Hmmm, right you are, assuming it takes ~8 cycles for a read (and if the 68k Clements book isn't lying also 8 for a write), at 8MHz, that's 8,000,000/8 cycles is ~1MB/s without anything else going on. Of course each of those reads should then be acted on and written back somewhere else in memory, so that's half that, so ~500KBps, and ofc the 68k has to execute code from other parts of RAM/ROM, so yeah, 250KBps seems like a reasonable value with all that going on, and certainly if wait states are inserted.
So that right there, I guess is the end of my trying to use a 232 or 2232. Oh well. Even with DMA, the timing cycles would be roughly the same - not that I want to use DMA as that would complicate things and I don't know enough about it to try right now.
On the other hand, I no longer have to worry about level shifters as 3.3V is off the table now, so that keeps it much simpler
Doing both lower and upper byte simultaneously would help I suppose.
Does FTDI have by some chance a 16 bit wide chip similar to the 245 without going to the way overkill ft601?
I'd be ok with using 2x245 if I can distinguish between the two ports, but yeah, there could be synchronization issues between lower and upper bytes. I suppose I could have the initial startup send two different values in the upper and lower ports, i.e. 0x12 to the low byte and 0x34 to the high byte or whatever and once read I know which is which, but ya, very kludgy. I suppose, I'd need to add a USB hub infront of the thing or just use two ports on the PC side.
Quote
You'll need a programmer for these devices. If you don't already have a somewhat general-purpose programmer, there are some good cheapies around. I like my XGecu TL866II Plus (~$60). There's probably a newer version (or two) by now.
I have this guy: https://www.amazon.com/gp/product/B00K73TSLM/ - it might work with the 22v10. It's a "Signstek TL866PLUS Universal USB MiniPro EEPROM Flash BIOS Programmer AVR GAL PIC SPI Support 40 Pin" - seems to be (almost?) the same thing you point to, likely just another vendor selling it. Doesn't say it has the "II" in the model, but scrolling down it says it does have that chip.