A couple of days ago I managed to get the clock looking much better with some capacitors and a small smoothing resistor. So, armed with my new oscilloscope, it was time to hook it back up to the rest of the system and see how things worked.

Short answer: they …

Following on from the last investigation into the mysterious decrement bugs I decided I'd done as much debugging as I could with just my old Saleae logic analyser, and took the plunge and bought an oscilloscope. I'm surprised I've managed to get away without having one for so long.

Once …

Since I added the hacked up display module, I've noticed an issue that's cropped up a few times. Since I haven't properly implemented reading the status register from the LCD controller yet, I've had to put small delay loops between character writes to avoid sending data too quickly. These are …

Some quick notes on debugging the new revision of the decode card:

• plugging card in prevents reset from making any progress. With the logic analyser it's clear that rst_trig is being triggered every clock cycle. This is because there's a bug in the logic for controlling the control memory daughter …

I had thought the MMU was pretty solid, since I gave it a good test after its v1.1 rework, and didn't find any issues. In testing the control unit, though, I've noticed some weirdness. Mapping addresses didn't work consistently. More often than not, about half the bits were incorrect …

Notes:

• low-temperature solder paste does not flow nearly as well as original version. Maybe because it's not thermally stable, and I'm not storing it at a constant temperature?

• short between VCC and GND after assembly and soldering. Removed 48 of 60 capacitors before finding the culprit on the 49th.

• bug …

The control lines are designed with a couple of common features:

• they all have a safe or no-op state when the lines are high. For simple lines, this means that they are active-low. For encoded lines, this means that all ones is a no-op command
• they all have pullup resistors …

I finally put together the MMU, the fourth of the seven PCBs that arrived in my August batch. A couple of things were obvious right off the bat:

1. I'd somehow screwed up the silkscreening, and all the text labels for the current MMU mode on the left of the board …

A big batch of PCBs arrived last week from China (7 different boards!), and I decided to have a go at the reset board first. This is a straightforward conversion of my breadboard prototype, so I thought it would be quick and easy to assemble and test, and I could …