Hi Roberto,

Keep going with the development board. Up to now I can't see any mistakes.
Until you will increase the clock speed you don't have to worry about
propagation delays, access memory or I/O time, gates type.... the real nightmare of developer.
To avoid troubles now, keep the CD1=1 and CD0=0, as by default.
Don't be tempted to enable the frequency multiplier in order to achieve 36Mhz (in your drawing you use XTAL 18Mhz).
The DS1270 it's not available with time access shorter than 70ns.
Thus your actual system will not work at 36Mhz. So, leave it at 18Mhz.
In the near future, try using 9,8304Mhz XTAL, enable the multiplier CD1=0, CD0=0, 4X/2X=1
and you will get 39,3216Mhz, as close as possible to 40Mhz.
In addition, you will not have any problems with setting different serial baud rates, working near allowed top speed.
This will reduce EMI and cost, as slower crystals are generally more available and thus less expensive.
Obvious, you have to take care of all times which now it doesn't matter (including new SRAM).
Inside are a lot of beautiful features you will discover step by
step (OFDE , RGSL , PFI bits).
Take as much as you can from HSM family beast.

Yes the 80C390 don’t need external reset capacitor. See the diagram on last page of 80C390.pdf data sheet.

After loading DPX with 0x20, you can read the switches state with MOVX A,@DPTR,
(where DPTR could have any value in the range 0x0000 - 0xFFFF, just because you use only one I/O location).
Alternatively you can use MOVX A,@Ri, after loading the MXAX with 0x20 value.

If the ROM loader is missing, the only solution to place the first program in the system is to load it in your additional PC programmer.


There is no need to apologize if your english is poor (in fact I have no complains about it).
One genuine english man told me the same thing. English is not my native language too.
I'm confident that other people joining this forum, understand what we are talking here.


Keep digging inside 80C390.

Silvio