Allen-Bradley 1771-IG(D) TTL Input Module
Allen-Bradley has two versions of the TTL compatible discrete Input modules that will interface to TTL output devices. The 1771-IG module will monitor eight TTL inputs while the 1771-IGD will monitor up to 16 inputs. Only the 1771-IG version has a 1ms input filter, while the 1771-IGD version has input diode protection to +5 volts and ground. The TTL voltage ranges are 0 - 0.5V DC for V low, and 2.7 - 5.25V DC for V high. The modules are current rated at I in low, 7mA source current (the device connected to the module must be able to sink this current and any current from pull up resistors), and I in high, 0.8mA (the module will sink this much current).
1771-IG(D) TTL Input Module Strapping
1771-IG TTL Input Module Strapping
Remove the module's left hand cover plate (the one without the labels). Observe the location of the configuration switches in figure 7.1. When selecting POSITIVE logic, switch 1 and 2 are generally set to the ON position. For NEGATIVE logic, switch 1 and 2 are generally set to the OFF position.
1771-IGD TTL Input Module Strapping
Remove the module's left hand cover plate (the one without the labels). Observe the location of the jumper figure 7.2. When selecting POSITIVE logic, set the jumper to the HIGH (left/rear) position. For NEGATIVE logic, set the jumper to the LOW (right/front) position.
1771-IG(D) TTL Input Module Installation
The Allen-Bradley 1771-IG(D) TTL Input Module may be installed in any Allen-Bradley Universal I/O Chassis, 1771-A1B, 1771-A2B, 1771-A3B, or 1771-A4B. Before Installation, calculate the power requirements of the modules currently in the chassis. Add to that 122mA @ 5V DC for the 1771-IG, or 50mA @ 5V DC for the 1771-IGD. Check to be sure that this combined current requirement does not exceed the current driving ability of the chassis power supply.
Only the 1771-IGD module has a fuse to protect the +5V DC power supply and the module's input terminals from the accidental application of voltage that could cause damage: voltage over 6.0V DC, reverse DC or AC voltage. Fuse rating: 0.5A at 250V, use Littelfuse 312.250 or similar.
The 1771-IG is not fuse protected so care must be taken to properly connect the power supply. Accidental application of AC, reverse DC, or over voltage could damage the module.
Module Location in the I/O Chassis
The 1771-IG(D) may be placed in any slot of the I/O chassis with the exception of of the extreme left slot. This slot is occupied by the Remote I/O Adapter Module. It is suggested that analog input modules and low voltage DC modules be placed away from AC modules or high voltage DC modules to minimize electrical noise interference.
The 1771-IGD has an additional restriction. EPICS software reads and writes the Allen-Bradly chassis in Two-slot addressing mode. A module group is considered to contain two Allen-Bradly slots. The first module group address is located at slot 0 and 1. The second is slot 2 and 3 and so on. When using a 16-bit input module in a two-slot addressing mode, the input module must always be inserted into an even number slot (left-hand side of the module group). A complementary output module (8-bit or 16-bit module) may be inserted into an odd number slot (right-hand side of the module group) completing the module group. If no complementary module is used then that slot must remain empty.
The 1771-IG has no such restriction. An 8-bit input module can be used with any 8-bit input or output module. There is no defined order as to which input or output module is inserted in a module group, and two inputs or two outputs can be used in the same module group. However, it is common practice when using an 8-bit input and an 8-bit output module in a module group, to insert the input module into the even (left-hand) slot and the the output module into the odd (right hand) slot of the module group.
The Allen Bradley Universal I/O chassis have the ability to limit the slot access to certain modules by the implementation of a keying system. Modules are slotted in two places at the edge of the circuit board. The position of the keying bands on the backplane connector of the I/O chassis must correspond to these slots. To key a slot for use by the 1771-IG TTL Input only, place the keying bands between 4 and 6 and between 34 and 36 on the I/O chassis backplane connector. To key a slot for use by the 1771-IGD TTL Input only, place the keying bands between 16 and 18 and between 24 and 26 on the I/O chassis backplane connector.
Before a module is inserted into the Universal I/O Chassis, be sure that the power to the chassis is shut off. This can be done without shutting off the IOC that the Universal I/O Chassis is connected to, and without removing the subnet communication link. To insert the module, place it in the plastic tracks on the top and bottom of the Universal I/O Chassis. Slide the module into the Universal I/O Chassis until the module comes in contact with the backplane connector. Do not force the module in, instead apply firm and even pressure on the module to seat it properly on the backplane connector. Snap the chassis latch over the top of the module and connect the wiring arm to the module. The Universal I/O Chassis should begin communicating with the host IOC when power is reapplied, no rebooting of the IOC will have to be done.
1771-IG(D) TTL Input Module Wiring Connection
Connecting field wiring to the 1771-IG(D) is accomplished through the use of a shielded cable to the wiring arm. Signals should be connected to the screw terminals on the wiring arm, as detailed in figure 7.3, and the wiring arm should be connected to the front tab connector on the 1771-IG(D). When shielded cable is used and grounding of the shield is desired, it is recommended that the connection be made at one of the I/O chassis mounting bolts. To prevent ground loops only the chassis end of the cable shield should be grounded.
1771-IG(D) TTL Input Module Use
The front panel on the 1771-IG contains nine red LED indicators. The top red LED labeled HIGH-TRUE indicates the module is selected for positive logic when illuminating. The next eight LEDs will indicate if an individual input is true.
The front panel on the 1771-IGD contains 18 LED indicators. The top green LED labeled ACTIVE indicates the module is connected to +5 volts and the fuse on the 1771-IGD is not blown. The next 16 red LED indicators, labeled 00 through 17 (octal), will indicate if an input is true. The last green LED labeled HIGH indicates the module is selected for positive logic when illuminating.