Feature: Embedded
Figure 6: Detail of Agon light’s board showing the return-path vias (pointed to) next to signal vias
to Vcc (or vice-versa) as the signals change layers, the return-path vias
also work as transfer vias, keeping the respective fi eld fringes locally contained as the signals move vertically around the board. T e most electromagnetically protected line in Agon’s board
is the serial transmitter (Tx) from the eZ80 to the ESP32 (Rx), as it is the key communication line between CPU and built-in terminal; see Figure 7. We use 33Ω in-series resistors on that line to absorb the higher frequency harmonics that may be refl ected due to impedance mismatches. T e line is also unidirectionally buff ered, as an extra layer of protection in case of fi rmware errors, and to allow for a high-impedance state disconnecting CPU from terminal. T e latter can be useful during fi rmware programming of the ESP32. T e schematics and board layout of Agon are available in its open-source repository. Although mostly envisioned as a self-contained, instant-on
microcontroller that dispenses with a host PC and sketch compilation,
Figure 7: Detail of Agon light’s board showing the system’s most protected line, running from right (eZ80 Tx) to left (ESP32 Rx)
Agon also excels as an 8-bit SBC, scoring by far the best in all common performance benchmarks. Figure 8 shows the result of only one of the benchmarks we ran, showing that Agon is 2.8x faster than the next best, a machine running at 28MHz – almost 10MHz faster than Agon’s clock. We envision Agon as a collective, unifying platform for both
microcontroller applications and retro computing. We do not sell it ourselves, but several entrepreneurs are either already doing so, or planning to do so shortly. T e high-fl exibility, high-performance, low-cost and open-source
nature of the project aims at providing a platform we can all call our own and help develop further. Nostalgic as it is, it is also a truly useful platform, fi lling an application niche hitherto unaddressed by alternative solutions: that of a self-contained, instant-on, BASIC- programmed microcontroller board that also happens to be the fastest 8-bit SBC ever created. So, join us and make Agon light your own!
Figure 8: Benchmark results (in seconds to completion) showing that Agon light, having completed the benchmark in just 1.8 seconds, is almost three times faster than the next-best system
www.electronicsworld.co.uk December/January 2023 23
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