Posts: 1
Joined: Mon Jul 03, 2023 7:37 pm

8155 timer frequency on Netronics Explorer 85

Hi. I'm improving the driver of the Netronics Explorer/85 computer. In particular, I want to enable the debugging functionality of the original ROM monitor, and for that I need a proper working 8155 timer. The problem I find is that the timer seems to be running at the 6.144MHz clock input of the 8085 and not at the 3.072MHz of the system clock.

The configuration for the 8085 is the following:

Code: Select all

I8085A(config, m_maincpu, 6.144_MHz_XTAL);

and for the 8155 is the following:

Code: Select all

i8155_device &i8155(I8155(config, I8155_TAG, 6.144_MHz_XTAL/2));
The 8155 works at half the frequency of the 8085 (in the real hardware the clk in of the 8155 is connected to the clk out of the 8085, and the clk out frequency of the 8085 it is 1/2 its x1, x2 oscillator input frequency).
Running experiments in MAME I see that the 8155 its decreasing its count as if its clock input was 6.144MHz.

Could you please give me a hint of how could I solve this?

Kind regards,


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