Two examples of Pro Mini clones, one with an 8 Mhz XTAL and 3V3 VREG and the other with a 16 Mhz XTAL and 5V VREG. Both have an ATMEGA328P micro-controller.

    DTR TXD RXD VCC GND GND
        PD1 PD0
TXD PD1                     RAW
RXD PD0                     GND
RST                         RST
GND                         VCC
2   PD2         PC5 A5  PC3  A3
3   PD3         PC4 A4  PC2  A2
4   PD4                 PC1  A1
5   PD5                 PC0  A0
6   PD6                 PB5  13 SCK
7   PD7  LED    RESET   PB4  12 MISO 
8   PB0  PB5    BUTTON  PB3  11 MOSI
9   PB1                 PB2  10
                PC6 PC7
            GND A6  A7

The above pinout is for the 3V3 example. The 5V example differs in that it places A5 and A4 alongside A6 and A7 at the bottom of the diagram.

We can power the boards with VCC up to 5V or utilise the RAW input which will feed the regulator.

A cp2104 serial module is well suited to connect to the pro mini and is able to supply both 3V5 and 5V for VCC. The photos show a cp2104 module in the background.

An arduino boot loader is present on these devices which communicates at 57600 baud. This is a reliable speed for a Pro Mini with an 8MHz XTAL but 115200 baud can be used on the 16 MHz device if the Optiboot boot loader is installed.

In the arduino IDE, the 3V3 device is selected as an `Arduino Pro or Pro Mini (3.3V, 8 MHz) w/ ATMEGA328'.

The Pro Mini doesn't have an ISP connector but we can wire and replace the boot loader, for example, with a USBasp.

VDD
GND
RESET 
MISO  PB4
SCK   PB5
MOSI  PB3