Siemens SM 321 Digital Input Modules

Every SM 321 variant, with current status and New Zealand availability. Fifteen article numbers on one page.

The SM 321 is the digital input module family for the SIMATIC S7-300 rack. It reads on/off field signals from limit switches, proximity sensors, pushbuttons and relay contacts and passes them to the CPU over the backplane. Variants differ by channel count, signal voltage, isolation grouping and whether diagnostics and process interrupts are supported.

Siemens discontinued the S7-300 platform, so every module here is spares-only. Most New Zealand plants running S7-300 are keeping the hardware in service rather than migrating, which means demand is for like-for-like replacements. We hold some of these lines and source the rest.

Every SM 321 variant

Taken from the Siemens S7-300 Module Data equipment manual.

Article number	Description	Inputs	Rated input voltage	Isolation	Diagnostics
6ES7321-1BP00-0AA0	DI 64 x DC 24 V, sinking/sourcing	64	24 V DC	groups of 16	No
6ES7321-1BL00-0AA0	DI 32 x DC 24 V	32	24 V DC	groups of 16	No
6ES7321-1EL00-0AA0	DI 32 x AC 120 V	32	120 V AC	groups of 8	No
6ES7321-1BH02-0AA0	DI 16 x DC 24 V	16	24 V DC	groups of 16	No
6ES7321-1BH10-0AA0	DI 16 x DC 24 V, High Speed	16	24 V DC	groups of 16	No
6ES7321-7BH01-0AB0	DI 16 x DC 24 V, hardware and diagnostic interrupts	16	24 V DC	groups of 16	Yes
6ES7321-7EH00-0AB0	DI 16 x DC 24/125 V, hardware and diagnostic interrupts	16	24 to 125 V DC	groups of 16	Yes
6ES7321-1BH50-0AA0	DI 16 x DC 24 V, source input	16	24 V DC	groups of 16	No
6ES7321-1CH00-0AA0	DI 16 x UC 24/48 V	16	24 to 48 V AC/DC	groups of 1	No
6ES7321-1CH20-0AA0	DI 16 x DC 48 to 125 V	16	48 to 125 V DC	groups of 4	No
6ES7321-1FH00-0AA0	DI 16 x AC 120/230 V	16	120/230 V AC	groups of 4	No
6ES7321-1FF01-0AA0	DI 8 x AC 120/230 V	8	120/230 V AC	groups of 2	No
6ES7321-1FF10-0AA0	DI 8 x AC 120/230 V, ISOL	8	120/230 V AC	groups of 2	No
6ES7321-7TH00-0AB0	DI 16 x NAMUR	16	24 V DC	groups of 2	Yes
6ES7321-7RD00-0AB0	DI 4 x NAMUR	4	24 V DC	see manual	Yes

The two NAMUR modules are documented separately in the Siemens ET 200M Signal Modules for Process Automation manual.

Watch the voltage, not just the channel count

This family spans 24 V DC, 48 to 125 V DC, 24 to 48 V AC/DC, 120 V AC and 120/230 V AC. Several variants have identical channel counts and very similar article numbers but completely different input voltages.

The 6ES7321-1BH02-0AA0 and the 6ES7321-1FH00-0AA0 are both 16-channel modules. One is 24 V DC, the other is 120/230 V AC. Fitting the wrong one does not work, and on a 230 V circuit it will not end well.

Read the number off the module, not off the drawing. Drawings go out of date and modules get swapped.

SIPLUS equivalents

SIPLUS modules are the extended environmental range versions, rated minus 25 to plus 60 or 70 degrees C with condensation permitted. Different article number, same function. Very few suppliers carry them.

SIPLUS article number	Standard equivalent
6AG1321-1BH02-2AA0	6ES7321-1BH02-0AA0
6AG1321-1BL00-2AA0	6ES7321-1BL00-0AA0
6AG1321-7BH01-2AB0	6ES7321-7BH01-0AB0
6AG1321-1FF10-7AA0	6ES7321-1FF10-0AA0
6AG1321-1CH20-2AA0	6ES7321-1CH20-0AA0
6AG1321-1FF01-2AA0	6ES7321-1FF01-0AA0
6AG1321-7RD00-4AB0	6ES7321-7RD00-0AB0
6AG1321-7TH00-4AB0	6ES7321-7TH00-0AB0

Do not forget the front connector

Every SM 321 ships without one. It is a separate article number.

Article number	Connector
6ES7392-1AJ00-0AA0	20-pin, screw terminals
6ES7392-1AM00-0AA0	40-pin, screw terminals
6ES7392-1BM01-0AA0	40-pin, spring terminals

The 64-channel 6ES7321-1BP00-0AA0 uses two 40-pin terminal blocks, not one. Tell us the module and we will include the matching connector in the quote.

What usually goes wrong

One channel dead, the rest fine. Usually an input opto-isolator, killed by a field short or an inductive spike. Module-level fault, not the CPU.

All channels reading high. Check the field supply common before condemning the module. A lifted 0 V return mimics a failed input and costs a lot of time.

SF LED lit. On the diagnostic variants, 6ES7321-7BH01-0AB0 and 6ES7321-7EH00-0AB0, that is a reported fault readable in the CPU diagnostic buffer. Read it before swapping hardware. On the non-diagnostic variants the SF LED will not help you, because those modules do not report.

Substituting one variant for another

Only two SM 321 variants support programmable diagnostics and process interrupts. If the original was a 7BH01 or a 7EH00 and the replacement is not, the engineer loses channel diagnostics and the CPU hardware configuration no longer matches.

Send us both numbers and we will tell you whether the swap will work before you buy.

Send us your article numbers

One module or a full project list. We will come back with price, condition and lead time. Quotes in NZD including GST.

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