The TMS370C156AFNT: It runs at 5 MHz and is supplied in a 68-pin PLCC package for surface-mount assembly. The part is ROMless — it has no internal program memory — so code must reside in external ROM, EPROM, or Flash accessed via the external bus. With 46 general-purpose I/O lines, an 8-channel 8-bit ADC, and serial interfaces (SCI and SPI), it targets industrial control and embedded systems where the designer controls the memory map and firmware is factory-programmed or loaded from an external serial Flash.
Because the TMS370C156AFNT is ROMless, every design using it must budget for an external memory device (typically a parallel EPROM or Flash) to hold the application code. This adds a second IC, extra PCB area, and a separate programming step. The trade-off is flexibility: you can change the firmware by swapping the external memory without respinning the MCU, and the external memory can be larger than any on-chip ROM the TMS370 family offered. For a production line, this means qualifying two components instead of one, and ensuring the external memory is available for the product's lifetime.
Industrial temperature grade and peripheral set
The on-chip peripherals include a PWM generator, a watchdog timer (WDT), and an 8-channel 8-bit ADC — enough for basic sensor readout and motor-speed control.
Lifecycle and sourcing posture
No last-time-buy risk is indicated on the current record.