I'm venturing out on a limb here but I don't believe the 245 is a latch...it is only a bi-directional buffer. Like its brother the 244 which is only one way, with its inputs on both side on the chip to ensure a messy layout. Note: I would always use a 245 en lieu of a 244 and tie the direction pin the way I need it. Cheers Mike -----Original Message----- From: Andy N1YEW [mailto:n1yew@SOFTHOME.NET] Sent: Tuesday, May 29, 2001 2:18 PM To: PICLIST@MITVMA.MIT.EDU Subject: Re: [PIC]: 8bit Data bus using a PIC16F84A.. A dream or reality? 74LS688 :-) i have a slight idea of what i am doing as i researched it..... the 74LS245 is used as a bus latch. later andy -- i used have no clue what i was doing. now i have a clue what i am NOT doing ;) ----- Original Message ----- From: "Dylan Hillier" To: Sent: Tuesday, May 29, 2001 10:19 AM Subject: [PIC]: 8bit Data bus using a PIC16F84A.. A dream or reality? > >sure it has enough pins ya just gotta use a 688 as a address comparator and > >an 8 bit bus latch :-) > > Im new to all this stuff... i know phillips makes such a device (668 > comapator) but i can never find a IC packaged 8 bit bus latch. Is there > such a thing or will i have to to make one from 8 d-flip-flops in parallel > with a common clock input and a tri-state enable input? > > Hrrmmm.. i thought u could use the 8 pins of PortB as the databus, 3 pins > of port A as the address bus (giving up to 8 devices ?), then use the > remaining 2 pins(Control Bus) of port A as I/O Read/Write. Then all u need > would be an address decoder IC and a set of tristate latches (input/output > latch) for each device (up to 8) for each device you plug onto the open > collector type bus? > > Keep in mind i have no idea what im doing.. im working off some pretty > strong assumptions here and i have no experience at all with pic's other > than writing simple software and controlling LCD (which i finally got to > work after 3 long hard weeks of pulling my hair out.) > > Someone mentioned memory mapped I/O, how does this differ from my above > mentioned scheme, does it mean there is a huge chunk of memory, and instead > of each device being on a bus it just writes to its own hard coded (in my > case) memory address, then the pic poles the addresses for device changes? > > This is all getting interesting.. > > > > > > >andrew -- i was gonna make a isa programmer but i shelved it > >----- Original Message ----- > >From: "Jim Robertson" > >To: > >Sent: Tuesday, May 29, 2001 6:40 AM > >Subject: Re: [PIC]: 8bit Data bus using a PIC16F84A.. is it possible. > > > > > > > At 01:40 PM 29/05/01 +0300, you wrote: > > > >On Tue, 29 May 2001, Dylan Hillier wrote: > > > > > > > >> > > > >> > > > > don't laugh please, James will be angry... > > > > > > > > > > > >> > > > >> Im hoping to use a PIC16F84A to do this with PortA as the > >address/control > > > >> bus and port B as the data bus. > > > >> I would like to ability to control up to 8 devices using the bus by > >simlpy > > > >> connecting them to the bus, much the same way as you would with an > >Device > > > >> Card in an ISA bus on a 'old school' PC. > > > >> > > > > Prototype reserved area for standard PC is 300H...31FH. > > > >You need some requirements: > > > >-- highZ for data signals > > > >-- address decoding pins, I think you can't do a full decode selection > > > > only with porta > > > >-- WR and RD signals > > > >-- no interrupts ? > > > >-- ISA bus frequency less than 8MHz ( available in old PC ) or a good > > > >software and 40Mhz pic > > > > > > > >I think there are other pic microcontrollers which will fit better your > > > >requirements. > > > > > > > >Vasile > > > > > > > > > Yes, I agree. One option would be to use a 17Cxx chip and memory mapped > > > I/O. You could also wait for the Romless 18Cxx chip and do likewise. > > > > > > I don't see that the '84 has enough I/O to do this comfortably. > > > > > > -Jim > > > > > > > > > > > > > > > > >-- > > > >http://www.piclist.com hint: The PICList is archived three different > > > >ways. See http://www.piclist.com/#archives for details. > > > > > > > > > > > > > > > NEWFOUND ELECTRONICS > > > mailto:newfound@pipeline.com.au > > > http://www.new-elect.com > > > MPLAB compatible PIC programmers. > > > > > > -- > > > http://www.piclist.com hint: The PICList is archived three different > > > ways. See http://www.piclist.com/#archives for details. > > > > > > > > > > > > >-- > >http://www.piclist.com hint: The PICList is archived three different > >ways. See http://www.piclist.com/#archives for details. > > -- > http://www.piclist.com hint: The PICList is archived three different > ways. See http://www.piclist.com/#archives for details. > > > -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.