Если кому интересно, то вот ответ от AD. Errata по ссылке http://www.caxapa.ru/files/errata702x_E2.pdf The connection in the diagram was in the original design but did not
function correctly.
The only way to use the DAC as a reference for the ADC is to connect the
DAC pin to the Vref input externally and select the external reference
connection.
The latest anomaly list for the ADuC702x is attached.