how to save memory to file in H8SX-1544 R5F61544FPV using jtag

FDT supports the H8SX-1544 using the E8a or straight RS232 in boot-mode:

Available MCUs' for Flash Development Toolkit

HEW would support the MCU in debug mode, it looks like it supports both E10A and E8a for H8SX-1544.

Target Device for E10A-USB(HS0005KCU01H/HS0005KCU02H)

but boot mode can only for programming  tts use uart 

That is correct, boot-mode only support programming, not debugging.

That is correct, boot-mode only support programming, not debugging.