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So my question is: is this a feasible way to replace the MCU, are there any other solutions that can be implemented with a reasonable cost, like a soldered flex cable, any ideas are most welcome, including a reliable source of reasonably priced HD6432345A20FA (aka H8S/2345). Because plan B is to just hijack the flex cable to the main-unit and make some kind of kludge just to control the radio part with a PC program.
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Are you sure that HD6432345A20FA is the part number of the failed MCU?
The Hitachi data sheet (page 893) shows this to be a mask ROM version:
Appendix F Product Code Lineup
Table F.1 H8S/2345 Series Product Code Lineup
Product Type Product Code Mark Code Package (Hitachi Package Code)
H8S/2345 Mask ROM HD6432345 HD6432345(***)TE 100-pin TQFP (TFP-100B)
HD6432345(***)TF 100-pin TQFP (TFP-100G)*
HD6432345(***)F 100-pin QFP (FP-100A)
HD6432345(***)FA 100-pin QFP (FP-100B)] ZTATâ„¢ HD6472345 HD6472345TE 100-pin TQFP (TFP-100B)
HD6472345TF 100-pin TQFP (TFP-100G)*
HD6472345F 100-pin QFP (FP-100A)
HD6472345FA 100-pin QFP (FP-100B)
F-ZTATâ„¢ HD64F2345 HD64F2345TE 100-pin TQFP (TFP-100B)
HD64F2345TF 100-pin TQFP (TFP-100G)*
HD64F2345F 100-pin QFP (FP-100A)
HD64F2345FA 100-pin QFP (FP-100B)
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Note: (***) indicates the ROM code.
Are you saying that you are planning to rewrite all of this MCU's firmware and replace the part with a flash version?