a bi-directional data channel based on the ic access-bus protocol is used for the communication between monitor and graphics board. in the case of a standard ibm vga compatible 15-pin monitor connector, pin 12 (formerly used as monitor id bit 1) is used for data transmission (sda), and the pin 15 (formerly used as monitor id bit 3) is used as transmission clock (scl). the graphics board can request the short edid information (see ddc1) as well as the more comprehensive vdif information (vesa display identification file).