Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!ginosko!ctrsol!cica!gatech!gitpyr!byron From: byron@pyr.gatech.EDU (Byron A Jeff) Newsgroups: comp.sys.m68k Subject: Re: What's the difference between the MC68661 and the MC68681? Message-ID: <9306@pyr.gatech.EDU> Date: 11 Oct 89 23:51:45 GMT References: <6735@hubcap.clemson.edu> Reply-To: byron@pyr.UUCP (Byron A Jeff) Organization: Georgia Institute of Technology Lines: 61 In article <6735@hubcap.clemson.edu> rchampe@hubcap.clemson.edu (Richard Champeaux) writes: -What's the difference between the MC68661 and the MC68681. Both are -serial drivers (UARTS). I have the data sheets for the 68661, but I -know nothing about the 68681. - -[describes 68661] -[describes difficulty interfacing 68661 to 68000] - -My definition of easy to interface to the 68000 is that it would accept -the 68000 control signals with a maximum of a few gates in between and -that it would either generate it's own DTACK or be fast enough to merely -use the chip select as the DTACK. - -I guess the interface circuitry isn't all that bad, but if the 68681 -does the same stuff (or more) and is easier to interface, I'd rather -use it. - -So, can anyone tell anything about the 68681? I don't need much info, -unless you want to tell me a lot about it. I basically would like to -know if it's easier to interface than the 68661, and if it's worth -pursuing. 68681 is a Dual UART with 68000 async interface. The only control circuitry you need to hook it up to a 68000 is an address decoder. It generates it's own DTACK. It nominally uses a 3.68 and change crystal but I've gotten 9600 using a 3.57 colorburst with no problem. Can't vouch for 19.2 and 38.4 however. In addition to the 2 serial ports which can be driven by the internal baud rate generator or by an external clock the chip also provides an 8 bit output port and a 6 bit input port with edge sensitive inputs that can generate interrupts. The 68681 supposedly can interface with the 68000 interrupt vector fetch but to be honest I have never gotten it to work (so I use autovector interrupts). My last application with the 68681 was a MIDI sequencer where I used one of the serial ports as a host port (9600 bps) and the other as a MIDI port (31250 bps). The midi clock was derived from the system clock. It worked like a charm (interrupt vector problems notwithstanding). One caveat from the first time I used it: you must let it generate it's DTACK in it's own good time. I put it in a 68008 test board that had a grounded DTACK and the 68681 screwed up it's read FIFOs (4 byte FIFO) when it didn't get it's DTACK. Other than that I love it. I'm using 4 of them in my next midi box (68010, 2 68008s, 1 Meg, 8 Midi ports) but that is another story. Hope this info helps. Let me know if I can be of any assistance. BAJ - -Thanks for any help. -Rich Champeaux (rchampe@hubcap.clemson.edu) -- Another random extraction from the mental bit stream of... Byron A. Jeff Georgia Tech, Atlanta GA 30332 Internet: byron@pyr.gatech.edu uucp: ...!gatech!pyr!byron