Programmable controller

A programmable controller, comprising:

• a base unit having a plurality of slots, or spaces where modules are to be mounted, arranged from a first end to a second end;
• and
• the modules mounted in the slots;
• wherein
• a slot connector that fits in a module connector of the module is provided in each of the slots, and the module is mounted in the slot by fitting the module connector on the slot connector,
• the modules include a master module that includes a function to start communication from the master module to another one of the modules at predetermined timing, and a slave module that includes a function to receive information through communication and perform communication to another one of the modules,
• the master module is mounted in one or more of the slots including the slot closest to the first end in a communication region, or a region including a plurality of the slots where the modules that perform the communication are to be mounted,
• the slave module is mounted in at least one of a plurality of the slots which are located closer to the second end than the one or more slots where the master module is mounted in the communication region,
• the communication includes forward communication that is started by the master module and that is performed so that the information is sequentially transmitted from the module on a first end side to the module on a second end side, and backward communication that is started by a second end module, or the slave module mounted closest to the second end, after the second end module receives the information in the forward communication, and that is performed so that the information is sequentially transmitted from the second end module to the master module,
• when the slave module mounted closest to the second end attempts to transmit the information received from the module on the first end side in the forward communication to the module on the second end side in the forward communication, this slave module detects that there is no module mounted on the second end side of this slave module, and recognizes that this slave module itself is the second end module,
• the base unit has forward communication wirings each connecting the slot connector on the first end side to the slot connector on the second end side out of the slot connectors adjoining each other in the communication region and performing the forward communication, and backward communication wirings each connecting the slot connector on the second end side to the slot connector on the first end side out of the slot connectors adjoining each other in the communication region and performing the backward communication,
• a forward switching unit and a backward switching unit are disposed near each of the slot connectors of intermediate slots, or the slots in the communication region excluding the one or more slots where the master module is mounted and the slot at the second end,
• the forward switching unit electrically disconnects the forward communication wiring on the first end side from the forward communication wiring on the second end side when the module is mounted in the slot, and electrically short-circuits the forward communication wiring on the first end side to the forward communication wiring on the second end side when the module is not mounted in the slot, and
• the backward switching unit electrically disconnects the backward communication wiring on the second end side from the backward communication wiring on the first end side when the module is mounted in the slot, and electrically short-circuits the backward communication wiring on the second end side to the backward communication wiring on the first end side when the module is not mounted in the slot.