// Build DAC lookup tables for 12-bit DACs.
    // MOS 6581: 2R/R ~ 2.20, missing termination resistor.
    build_dac_table(model_dac[0], 12, 2.20, false);
    // MOS 8580: 2R/R ~ 2.00, correct termination.
    build_dac_table(model_dac[1], 12, 2.00, true);

// The SID DACs are built up as follows:
//
//          n  n-1      2   1   0    VGND
//          |   |       |   |   |      |   Termination
//         2R  2R      2R  2R  2R     2R   only for
//          |   |       |   |   |      |   MOS 8580
//      Vo  --R---R--...--R---R--    ---
//
//
// All MOS 6581 DACs are missing a termination resistor at bit 0. This causes
// pronounced errors for the lower 4 - 5 bits (e.g. the output for bit 0 is
// actually equal to the output for bit 1), resulting in DAC discontinuities
// for the lower bits.
// In addition to this, the 6581 DACs exhibit further severe discontinuities
// for higher bits, which may be explained by a less than perfect match between
// the R and 2R resistors, or by output impedance in the NMOS transistors
// providing the bit voltages. A good approximation of the actual DAC output is
// achieved for 2R/R ~ 2.20.
//
// The MOS 8580 DACs, on the other hand, do not exhibit any discontinuities.
// These DACs include the correct termination resistor, and also seem to have
// very accurately matched R and 2R resistors (2R/R = 2.00).