View of the 8252 development board and peripherals connected.
Here you see the three main connections to the 8252 development board.
The top lead is the serial connection, going to the PC, via an RS-232 chip (in the matchbox wrapped in green tape).
The middle interface is shown with an LCD (16 chars by 2 lines) connected. This is the main application interface, and provides 12 I/O lines to interface with.
The lower connector shown is a pair of (red & black) wires for the +5 V supply to the board. I used a connector compatible with a spare PC PSU.
Clearest view of entire board.
The switch is shown in the mode for running external memory ie. in the external 28-pin memory chip. When the switch is in the upper position then the lower 8 k of the program memory map is internal.
The button is the reset button, which begins program execution at address 0000 h. In internal mode, this means the internal downloader program is run, to accept a new program (hex file) from the PC into the external memory chip, and in the external mode this means the downloaded target program (development code) is executed.
Angle view.
You can make out that I've used a stack of 40-pin IC sockets for the micro, for the occassion I remove the chip. One socket is left 'permanently' connected to the chip, acting as a 'sacrificial' socket to protect the chips' pins, ant the other left in the socket, reducing plug/unplug damage to the socket. As these are 'sacrificial' sockets, they can be replaced should any damage come to them during plugging/unplugging, without harm coming to the chip or the socket in the board, which would be a real hassle.
On the bottom left of the board you can see two wire links appearing as loops. These are ready crocodile (alligator) clip points providing Ground and +5 V, which are handy for clipping my logic probe, etc. on to.
The two sockets on the board's right (unpopulated at this stage) are for the two chips that allow port expansion, via the three sockets (backs shown) on the board's bottom right.
Example peripheral setup with development board.
This is the main part of the 8252 development board.
This is the only part of the board you actually have to make, the rest (two chips and three or more 12-way connectors) shown in the other pictures is an optional port expansion.