The HT66F0021 and HT66F0031 devices include 1K×14 bits of Flash Program Memory while the HT66F0041 includes 2K×14 bits of Flash Program Memory. These devices all have 64 bytes of SRAM, 32×14 bits of emulated EEPROM, an operating voltage of 1.8V~5.5V, a fast 4-channel 10-bit resolution A/D Converter, a Timer Module and an 8-bit PWM output. Two fully internal oscillator options are provided, one is an 8MHz HIRC and the other is a 32kHz LIRC. The integrated high resolution HIRC oscillation circuit has a resolution of ±0.5% under the conditions of fixed voltage and fixed temperature while the LIRC has a resolution of ±1%.

With regards to packaging, the HT66F0021 is supplied in an 8-pin SOP package type, the HT66F0031 is supplied in a 16-pin NSOP package type while the HT66F0041 is supplied in 16-pin/20-pin NSOP and 20-pin SSOP package types. Using these minimal size package types makes these devices very suitable for use in small profile household appliances.