Little update,
pretty much proved the device works as expected, missed a pull up resitior off, and a capacitor LOL.
i still plan to produce 2 versions, standard and enhanced
Standard version plug in and go. composite video 1v p-p into a 75 Ohm load ( most tv's and monitors)
Enhanced version will be approx. GBP 5 more expensive (different chip ) and will offer Clock doubling, inverse video, inverse border, M1not, and a constant 3.25Mhz output for people with zonx or other sound cards that need the clock. of course to use these features 5 extra wires need soldering to connect the address lines that are not present at the ULA socket.
Things that are different between this enhanced version and my really old altera design ( that had clock doubling ) .. The reset wire and resistor are gone. you can still lock the features set but resetting requires a) a power cycle. or b) exciting code at memory address 0. i.e an external system reset, causing the cpu to start exciting code at address - or a deliberate RAND USR 0 .
Clock doubling in FAST mode still requires a POKE 1001,x ( x doesn't matter) but you no longer need to set a feature bit to allow this.
Rompatch is also automatic, this allow easier switching back to slow mode from fast when in clock doubled mode.
so currently the control bits are as follows,
we now have 2 spare bits.... what to do with them ???
Code: Select all
//=================================================================================
// FOR REFERENCE
//
// bit 0, 0 == normal operation of poke code,
// 1 == lock this setting (all bits of this write cycle locked)
// (RESET BY a RESET automatically genrated whenn cpu excutes instruction at memory location zero)
//
// bit 1, 0 ==
// 1 ==
//
//
// bit 2, 0 == uk/us select read normally
// 1 == uk/us select read inverted
//
// bit 3, 0 ==
// 1 ==
//
// bit 4, 0 == Video normal
// 1 == Video inverted // video and border
//
// bit 5, 0 == border normal
// 1 == border inverted // just border
//
// bit 6, 0 == M1not disabled
// 1 == M1not enabled
//
// bit 7, 0 == Turbo Off
// 1 == turbo On // also activates Rompatch, patches 1 byte in rom to allow easier switching from fast to slow in basic
finally i estimate ( and thius is a rough guess based on todays prices )
Standard ULA to cost
20 GBP + postage cost (currently GBP 8.75 to most of Europe)
Enhanced ULA to cost
25 GBP + postage cost (currently GBP 8.75 to most of Europe)
Those wires... (if ya know, ya know !)
regards Andy
P.s those faint diagonal lines seem to be a rolling shutter effect and you cant see them in real life )
what's that Smell.... smells like fresh flux and solder fumes...
nobody wants stinky 3.3v stuff 
