Further to the above:
Obviously as the name suggests, the BSCU can only control the level of wheel braking to meet the target selected - not the maximum overall aircraft deceleration. So if for example autobrake "1" was selected (a target decel of 4 ft/sec/sec) and all manner of decel methods were employed (select reverse, deploy speedbrakes, land on an upslope, land in quicksand, land and have all the passengers put their feet out on the ground or land and deploy a braking parachute) which resulted in a decel rate of say 5ft/sec/sec then there is nothing that the BSCU can do about it. In this case it will command nil Hyd Press to the brake units as it "sees" the required decel rate and is fat, dumb and happy.