{"product_id":"allen-bradley-plc-5-1775-l4-main-processor-module","title":"Allen-Bradley PLC-5 1775-L4 Main Processor Module","description":"\u003cp\u003eThe \u003cstrong\u003eAllen-Bradley 1775-L4\u003c\/strong\u003e, also cataloged as the \u003cstrong\u003e1775-L\u003c\/strong\u003e main processor module, operates as a dedicated hardware component for executing ladder scan and I\/O supervision across the PLC-3\/10 peripheral bus within 1775-A3 chassis systems.\u003c\/p\u003e\n\u003ch3\u003eCatalog Number Decoding\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e\n\u003cstrong\u003e1775-\u003c\/strong\u003e: PLC-3\/10 chassis and processor family\u003c\/li\u003e\n\u003cli\u003e\n\u003cstrong\u003eL4\u003c\/strong\u003e: Level-4 main CPU for PLC-3\/10, 16-bit custom ASIC, 2K-word data table baseline\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eHardware Specifications\u003c\/h3\u003e\n\u003cfigure\u003e\n\u003ctable\u003e\n\u003cthead\u003e\n\u003ctr\u003e\n\u003cth\u003eParameter\u003c\/th\u003e\n\u003cth\u003eSpecification\u003c\/th\u003e\n\u003c\/tr\u003e\n\u003c\/thead\u003e\n\u003ctbody\u003e\n\u003ctr\u003e\n\u003ctd\u003eModel\u003c\/td\u003e\n\u003ctd\u003e1775-L4\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eBrand\u003c\/td\u003e\n\u003ctd\u003eAllen-Bradley\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOrigin\u003c\/td\u003e\n\u003ctd\u003eUSA\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eWeight\u003c\/td\u003e\n\u003ctd\u003e2.74 kg\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eShipping Dimensions\u003c\/td\u003e\n\u003ctd\u003e6.5 x 33.5 x 49 cm\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eOperating Temp\u003c\/td\u003e\n\u003ctd\u003e0 to 60 deg C\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eStorage Temp\u003c\/td\u003e\n\u003ctd\u003e-40 to 85 deg C\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eHumidity\u003c\/td\u003e\n\u003ctd\u003e5-95 % RH non-condensing\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eVibration\u003c\/td\u003e\n\u003ctd\u003e1 G at 5-150 Hz\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eProcessor Type\u003c\/td\u003e\n\u003ctd\u003e16-bit custom ASIC\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eScan Time\u003c\/td\u003e\n\u003ctd\u003e10 ms per 1K instructions (boolean)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eData Table Memory\u003c\/td\u003e\n\u003ctd\u003e2K words (expandable via 1775-MS4\/MS8\/MSA)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eDiscrete I\/O Capacity\u003c\/td\u003e\n\u003ctd\u003e8192 points max\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eData Highway\u003c\/td\u003e\n\u003ctd\u003e57.6 kbps peer-poll, twinax, 32 nodes max\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eRemote I\/O\u003c\/td\u003e\n\u003ctd\u003e1.544 Mbps scanner mode\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003eProgramming Port\u003c\/td\u003e\n\u003ctd\u003eRS-232 (DF1, 1770-T4 \/ 6200 software)\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003ctr\u003e\n\u003ctd\u003ePower Source\u003c\/td\u003e\n\u003ctd\u003e5 VDC backplane from 1775-P2\/P3 supply\u003c\/td\u003e\n\u003c\/tr\u003e\n\u003c\/tbody\u003e\n\u003c\/table\u003e\n\u003c\/figure\u003e\n\u003ch3\u003ePLC-3 Peripheral Bus Coupling and Firmware Lock\u003c\/h3\u003e\n\u003cp\u003eThe 1775-L4 seats in the dedicated CPU bay of a 1775-A3 chassis and draws 5 VDC from the 1775-P3 power supply; it is not 1785-Lxx pin-compatible and will not seat in a 1771 PLC-5 rack. Execution closes over the PLC-3 peripheral bus at 10 ms\/K instruction scan, with I\/O mapped through a 1775-SR5 or 1775-S4 scanner module—not directly on the backplane. Firmware is mask-ROM fixed; no flash update path exists. Memory expansion uses 1775-MS4 (32K) \/ MSA (64K) daughter cards stacked on the CPU header. EtherNet\/IP, ControlNet and Profinet licences are absent—networking is limited to DH 57.6 kbps twinax and 1.544 Mbps RIO. Backplane bus velocity licence does not apply; this is a 1980s 16-bit peripheral-bus CPU, not a ControlLogix rack module.\u003c\/p\u003e\n\u003ch3\u003eOrdering Info\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003e1 x 1775-L4 main processor module (discontinued 2014-04-29, surplus sealed unit)\u003c\/li\u003e\n\u003cli\u003e1 x 1775-MS4 32K memory daughter card (optional, not fitted)\u003c\/li\u003e\n\u003cli\u003e1 x 1775-CAK front-panel interconnect cable (field-supplied)\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eChassis Mounting and Bus Rules\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eSeat CPU in the leftmost designated processor bay of 1775-A3 chassis; do not occupy I\/O scanner slot with the L4.\u003c\/li\u003e\n\u003cli\u003eFeed 1775-P3 power supply from isolated 115\/230 VAC, 5 VDC backplane rail must settle at 5.0 VDC +\/-0.25 V before CPU insert.\u003c\/li\u003e\n\u003cli\u003eTerminate DH twinax (Belden 8723) with 75 ohm resistors at both trunk ends; max 32 nodes, max 7000 ft trunk.\u003c\/li\u003e\n\u003cli\u003eRS-232 programming port uses 25-pin D-sub to 1770-T4 terminal or PC null-modem; DF1 protocol at 9600\/19200 bps.\u003c\/li\u003e\n\u003cli\u003eBond 1775-A3 chassis ground to cabinet ground bus with 4 mm² green\/yellow, single point only.\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003eFrequently Asked Questions\u003c\/h3\u003e\n\u003cp\u003eQ: Can the 1775-L4 be inserted into a PLC-5 1785 rack?\u003c\/p\u003e\n\u003cp\u003eA: No. Edge connector keying and backplane signaling differ. 1775-L4 runs only in 1775-A3 (PLC-3\/10) chassis. Forcing into 1771-A3B bends the 5 VDC tabs and leaves the 1785 bus undriven.\u003c\/p\u003e\n\u003cp\u003eQ: Is the module hot-swappable on a live 1775 backplane?\u003c\/p\u003e\n\u003cp\u003eA: No. 5 VDC backplane insertion arcs the ASIC power pins and corrupts the peripheral bus arbiter. PLC-3\/10 requires 1775-P3 power off before CPU extraction or insertion.\u003c\/p\u003e\n\u003cp\u003eQ: How is user memory expanded beyond 2K words?\u003c\/p\u003e\n\u003cp\u003eA: Stack 1775-MS4 (32K), 1775-MS8 (32K) or 1775-MSA (64K) CMOS RAM daughter cards on the CPU header. Data table then spans base 2K plus daughter card space; no firmware change needed.\u003c\/p\u003e\n\u003cp\u003eQ: What scan time applies to 4K boolean instructions?\u003c\/p\u003e\n\u003cp\u003eA: 10 ms per 1K instructions nominal, so 4K executes in 40 ms per full scan. Timer\/counter and PID blocks add overhead; actual wall-clock scan is 10-15% longer than pure boolean math.\u003c\/p\u003e\n\u003cp\u003eQ: Does 1775-L4 support DH+ (Data Highway Plus)?\u003c\/p\u003e\n\u003cp\u003eA: No. It speaks original DH at 57.6 kbps half-duplex peer-poll over twinax. DH+ (1784-KT\/XT) is a PLC-5 era protocol; bridging requires a 1775-KA to DH then a 1784-KF2 gateway.\u003c\/p\u003e\n\u003cp\u003eQ: Can RS-232 port run while DH trunk is active?\u003c\/p\u003e\n\u003cp\u003eA: Yes. RS-232 is independent DF1 point-to-point for programming\/HMI; DH trunk runs peer-poll concurrently. Both share the 16-bit ASIC but separate UART blocks; no arbitration conflict.\u003c\/p\u003e\n\u003cp\u003eQ: What replaces 1775-L4 in a migration?\u003c\/p\u003e\n\u003cp\u003eA: No drop-in. PLC-3\/10 migrates to ControlLogix 1756-L7x with 1783-ETAP DH+ tap and 1756-DH\/DHRIO bridge modules. Ladder translates via RSLogix 5-\u0026gt;5000 conversion, not binary lift.\u003c\/p\u003e\n\u003cp\u003eQ: Battery backup on 1775-L4?\u003c\/p\u003e\n\u003cp\u003eA: No on-board battery. CMOS RAM (1775-MS4\/MSA) holds data only while 1775-P3 5 VDC rail is alive; on total power loss data table clears. Program resides in mask-ROM; reload via 6200 software from tape\/PC.\u003c\/p\u003e","brand":"Allen-Bradley","offers":[{"title":"Default Title","offer_id":46066445680813,"sku":"1775-L4","price":88.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0733\/1613\/9181\/files\/allen-bradley_1775-l4.jpg?v=1786347442","url":"https:\/\/www.maxwellplc.com\/ga\/products\/allen-bradley-plc-5-1775-l4-main-processor-module","provider":"Maxwell PLC Ltd","version":"1.0","type":"link"}