Rushing ...
Antiphase PWM per motor looks OK.
Disabling IC using EN lines will often create large motor spike - as long as internal IC catch diode rating is OK that's OK. Otherwise add external diodes to supplies.
What battery chemistry. What size?
AA Alkaline will often tolerate significant regeneration.
Unless battery is small physically or you want exceptional shelf life then NimH will be better than Alkaline. For very long shelf life LSD NimH are getting very good.
At AA size, energy density of NimH now equals or exceeds Alkaline and high load dishcharge characteristics are much superior so there is little reason for Alkaline.
At small cell size Alkaline MAY make sense.
I have not tried this
Answer is "seems like this to me".
Caveat emptor :-):
Motor inductance and resistance will set t = L/R time constant. But, very easy to put small resistor from motor to ground, apply voltage and watch voltage in resistor and thus current rise on scope. PWM period which is small compared to total motor rise time will (probably) be good.
If you take the logic step by step, let's say:
ENA = 1, IN1 = 1, IN2 = 0
(left is the IN, right the EN input, ~ stands for inverted by the bubble)
So the top left AND gate:
1 + 1 = 1
bottom left AND gate:
~1 + 1 = 0
Top right AND gate:
0 + 1 = 0
Bottom right AND gate:
~0 + 1 = 1
So in this case the top left and bottom right transistor are turned on.
Best Answer
With two pins you have full control. This allows both forward, reverse and stop. if you want to allow coasting, you will need three pins to bring Ven low. If you do not need fast stop, you could use an XOR to control the Ven from the 2 control lines. When they are equal drive t low. Then it has forward reverse and coast.
If you hold Ven High when you decide to stop moving it will full brake. If you use a simple XOR gate to do the Ven signal then you can only coast. It is decided based on what you want the motor to do. If you need the option, use three lines. from a micro this is almost no cost.