HCU04

U9A and U9B in region D2 of the jwdonal schematic

U9C, U9D, U9E, and U9F, in region A3 of the jwdonal schematic

The HCU04 is a hex inverter. The first two inverters take SCLK from pin 41 of S-DSP as input:

• U9A outputs CIC3 to the Cartridge Slot
• U9B outputs CL1 to the CIC

The next two inverters help generate XIN:

• U9C appears to undo the inversion that U9C did, and sends the output to R5, which eventually becomes XIN after passing by the pull-down R4
• U9D is in parallel with R6, receiving its input from C4 and outputting to U9C

The last two inverters take ground as input and their outputs are not connected:

• U9E
• U9F