The Velleman K8048 is long-standing board that incorporates a serial port programmer and experimenter's I/O section of LEDs and switches.

Although the interface connects to the serial port, it doesn't utilise the RS-232 serial protocol and instead programming is performed using bit-banging.

The bit-bang programmer has the following serial interface characteristics (D-SUB-9).

 D-SUB-9
 -------
 1 2 3 4 5
  6 7 8 9

 1:CD          ICSP
 2:Rx          ----
 3:Tx      =>  1 !MCLR / VPP
 4:DTR     =>  4 PGD
 5:GND           GND
 6:DSR
 7:RTS     =>  5 PGC
 8:CTS     <=  4 PGD
 9:RI

Data output bits are sent through the DTR line and clocked on the falling edge of RTS.

The Tx line is utilised to enable the application of the high programming voltage on !MCLR/VPP and not for sending data bits.

Data input bits are read from the CTS line using the same clock as for output with the data output line taken high for correct circuit operation.

 Socket    8-pin     14-pin    18-pin    28-pin
 --------- --------- --------- --------- ---------
 Function  Pin
 --------- ---
 LD1       GP2 (5)   RC0 (10)  RB0 (6)   RA0 (2)
 LD2       GP4 (3)   RC1 (9)   RB1 (7)   RA1 (3)
 LD3                 RC2 (8)   RB2 (8)   RA2 (4)
 LD4                 RC3 (7)   RB3 (9)   RA3 (5)
 LD5                 RC4 (6)   RB4 (10)  RA4 (6)
 LD6                           RB5 (11)  RA5 (7)

 SW1       GP5 (2)   RC5 (5)   RA0 (17)  RB0 (21)
 SW2                 RA2 (11)  RA1 (18)  RB1 (22)
 SW3                           RA2 (1)   RB2 (23)
 SW4                           RA3 (2)   RB4 (25)

 PGD       GP0 (7)   RA0 (13)  RB7 (13)  RB7 (28)
 PGC       GP1 (6)   RA1 (12)  RB6 (12)  RB6 (27)
 VPP       GP3 (4)   RA3 (4)   RA5 (4)   VPP (1)
 PGM/24                                  RB3 (24)
 PGM/26                                  RB5 (26)

 OSC1                RA5 (2)   RA7 (16)  RA7 (9)
 OSC2                RA4 (3)   RA6 (15)  RA6 (10)

 VDD/VCC   VDD (1)   VDD (1)   VDD (14)  VDD (20)
 VSS/GND   VSS (8)   VSS (14)  VSS (5)   VSS (8, 19)

 NC                            RA4 (3)
 NC                                      RC0 (11)
 NC                                      RC1 (12)
 NC                                      RC2 (13)
 NC                                      RC3 (14)
 NC                                      RC4 (15)
 NC                                      RC5 (16)
 NC                                      RC6 (17)
 NC                                      RC7 (18)

 SK3
 ---------
 5 4 3 2 1

 1:VPP 12V
 2:VDD 5V
 3:VSS/GND
 4:PGD
 5:PGC

 Voltage levels (No chip installed, no D-SUB-9 connection)
 ---------------------------------------------------------

 Switch set to RUN.

 1:VPP          5V
 2:VDD          5V
 3:VSS/GND      0V
 4:PGD          5V
 5:PGC          5V

 Switch set to STANDBY.

 1:VPP          0V
 2:VDD          0V
 3:VSS/GND      0V
 4:PGD          5V
 5:PGC          5V

 Switch set to PROG.

 1:VPP          12V
 2:VDD          5V
 3:VSS/GND      0V
 4:PGD          5V
 5:PGC          5V

Velleman K8048