8048 and MCS-48 made designing with Microprocessors easy with built in I/O ports, RAM and Timer. The I/O ports for the 8085 was an external 8255. 8749 enabled users to burn and test firmware on an integrated UV Eprom.
80C51-52 which came out as the fully evolved uC had built in Serial Ports UART and more Math, better Timer-Counter and Interrupt Handling. The 'C' is for CMOS that made handheld instruments possible due to low battery usage and lesser support chips.
Here is a kit from Bipom that may help you learn more about the basics of embedded systems with a SBC,
MicroTRAK Bipom 51-E Complete
MicroTRAK/51-E Complete includes MicroTRAK Carrier Board, MINI-MAX/51-E Microcontroller Board with Ethernet, TB-1 Training Board, MMC-RTC-1 board with Real-Time Clock and 128MB Multimedia Card (MMC), 8051 I/O Module
The Assembly Code MCS-51 set is used to program the chip. There is a 8052 Basic that can understand the Basic Language, useful for people who are not comfortable with mnemonics.
Now we have 8051 chips with EE Flash and some have a watchdog and I2C too.
80C51, SBC, Firmware and Circuits
80C51 Single Board Computer SBC and Firmware Code. Interface 8051 or 8052 to PC on a RS-232 or serial port. Microcontroller Board and learn about MCS-51.
delabs circuits - micro1