Fixed #345, Fixed #267.

Marlin/Configuration.h

 // PID settings:
 // Comment the following line to disable PID and enable bang-bang.
 #define PIDTEMP
-#define PID_MAX 255 // limits current to nozzle; 255=full current
+#define PID_MAX 256 // limits current to nozzle; 256=full current
 #ifdef PIDTEMP
   //#define PID_DEBUG // Sends debug data to the serial port. 
   //#define PID_OPENLOOP 1 // Puts PID in open loop. M104/M140 sets the output power from 0 to PID_MAX
 
 // This sets the max power delived to the bed, and replaces the HEATER_BED_DUTY_CYCLE_DIVIDER option.
 // all forms of bed control obey this (PID, bang-bang, bang-bang with hysteresis)
-// setting this to anything other than 255 enables a form of PWM to the bed just like HEATER_BED_DUTY_CYCLE_DIVIDER did,
+// setting this to anything other than 256 enables a form of PWM to the bed just like HEATER_BED_DUTY_CYCLE_DIVIDER did,
 // so you shouldn't use it unless you are OK with PWM on your bed.  (see the comment on enabling PIDTEMPBED)
-#define MAX_BED_POWER 255 // limits duty cycle to bed; 255=full current
+#define MAX_BED_POWER 256 // limits duty cycle to bed; 256=full current
 
 #ifdef PIDTEMPBED
 //120v 250W silicone heater into 4mm borosilicate (MendelMax 1.5+)