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The MC6802 has 128x8 on-chip RAM ..
However, this RAM can be enabled (by RE = RAM Enable pin) to respond to the MCU controls or can be disabled and thus de-facto not present ..
Therefore it is called "optional" .. (see description of this RAM in the MC6802 data sheet: https://www.datasheets.org.uk/search.php?q=MC6802&sType=part )