Need to know if it is an 6"I" 2.3L (4 cylinder) or the 6"S" 3.0L (V-6) ?
ADDED: thanks for the additional information as this does matter on this vehicle,
The Mazda Service manual says this code is: Key on or engine running; and the PCM detected that the Battery Positive voltage circuit to the PCM was less than 2.50v, condition met for 2 seconds. Did your battery discharge? This could also be caused by a blown EEC fuse, corroded connector pins at the PCM connector or the worst case a failed PCM!
Try to clear the emission related data and see if the code recurres!