The problem I'm really having is dealing with using the D-flip flop.....and the details around the synchronous preset.... My assumptions were pretty much as follows: 1) That the clock input was leading edge triggered, and that on that edge the value of the D input gets transfered to Q. 2) That if the asynchronous reset goes high at any point, that Q goes low, and stays low until both the reset is released, and something else happens to set Q back high (like D being high on an edge). 3) That the synchronous preset is basically a way to force Q to a 1 state when the clock edge occurs... but I have a feeling that this is wrong, since you could do the same thing by forcing the D input high. Although I've worked around needing a registered output at all in my design at this point, I'd still like to be able to find this while I'm dealing with it, so I can file it with the pal documentation. I'd really love a table which has columns for D, CLK, AR, SP, and Q, and shows the value of q for each set of inputs.... aka: D CLK AR SP Q X X H X L H ^ L X H etc. -forrest Richard Seriani wrote: > Forrest, > > The Lattice Semiconductor datasheet seems to cover the output logic > macrocells pretty thoroughly > http://www.latticesemi.com/lit/docs/datasheets/pal_gal/22v10.pdf > > Can you describe something more specifically that is missing from/unclear in > the documentation? I have a text or two that provide some coverage of the > these devices, but not much more than what is in the datasheet and the usual > sum-of-products PLD programming. > > Richard > > > ----- Original Message ----- > From: "Forrest W Christian" > To: "Microcontroller discussion list - Public." > Sent: Wednesday, December 02, 2009 5:24 AM > Subject: [EE] 'truth table' for GAL22V10 registered outputs > > > >> I'm trying to use a flip-flop in a GAL22V10 and am having problems with >> making it do what I want. >> >> The output cell on a 22V10 basically is a D flip-flop with asynchronous >> reset, and synchronous preset, which seems straightforward enough. >> Unfortunately it doesn't seem to be working the way I'd expect..... So, >> I went looking for some documentation... which I sure haven't been able >> to find. I'm sure I'm making some incorrect assumption about this >> particular D flip-flop, but without docs it's proving difficult to >> figure out. >> >> Is someone aware of a truth table or similar for the output register on >> a 22V10? >> >> Thanks, >> >> -forrest >> -- >> http://www.piclist.com PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> >> > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist