When a supercapacitor is connected to VBB, the memory can be maintained anywhere from a couple days to a couple weeks once powered off. The CB290/CB405 consumes about 15-20mA of current when idling. For a longer backup period, a battery pack can be used. A protection diode, as shown below, is necessary when using a battery, as the device normally attempts to charge a capacitor through VBB. Due to the relatively high standby current for battery backup, it is recommended to keep the device powered if possible and only maintain battery backup for short periods in the case of an emergency.
If a CUBLOC module is supplied with power above the recommended voltage, the device can be destroyed. Also please be careful to avoid electrostatic discharge, as it too can destroy the device. Please be aware that P1 is an input-only pin. To reduce accidental power drain, please set unused pins to input. All I/O ports are set to input as default at power on. When not using SIN, SOUT, and ATN, please do not connect them to anything.
The CT1721C will maintain data in its volatile memory when powered off by using a backup battery. If backup is not needed, the program should clear the memory at the beginning of the program.
Const Device = CT1720 Dim TX1 As Integer, TY1 As Integer TY1 = 0 ' Clear only TY1
Use RamClear to clear all data memory at the start of your program.
Const Device = CT1720 Dim TX1 As Integer, TY1 As Integer RamClear ' Clear all RAM, both TX1 and TY2
To add a backup battery to the CT1721C, connect a 3V battery to the “Batt. Backup” terminal on the back, bottom right side of the CT1721C and leave the “JUMPER_SUPERCAP” open. To use a super capacitor instead of battery, connect the super capacitor to “Batt. Backup” and short the “JUMPER_SUPERCAP” terminal to enable charging while the power is on.
In Ladder Logic, all registers S, M, C, T, and D are retained by the backup battery. Register P is cleared by default when the device is powered on. If you only want to clear parts of a register, rather than all registers, use the following method:
Const Device = CT1720 Dim i As Integer For i=0 to 32 ' Clear only M0 to M32 _M(i) = 0 Next Set Ladder On