Just in case the information at the website didn't tell you everything. The main differences are: 1. The 1200 does 88 I/O, 1500 128 I/O (discrete) 2. 1200 only one comm port, 1500 can have two 3. with two ports the 1500 has seperate memory for data logging. 4. 1200 has smaller foot print 5. 1500 I/O has prewired terminal blocks.