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Ramtron Processor Companions are complete support and peripheral solutions with highly integrated mixed signal (analog and digital) functions for processor-based systems. Never before has a solution combined the fast read/write performance and unlimited endurance of nonvolatile F-RAM (ferroelectric random access memory) with a real-time clock (RTC), processor supervisor, and other common peripherals. |
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SPI Processor Companion
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| Part | Vdd | Interface | Memory | RTC | RTC Alarm | Power Monitor | Watch Dog | Early Power Fail | Serial Number | Battery Switch Over | Event Detect | Package |
 FM33256B | 3V | SPI | 256Kb |  | | | | | | | Count | SOIC14 |
 FM33256 (NRND) | 3V | SPI | 256Kb |  | | | | | | | Count | SOIC14 |
| FM3316 (NRND) | 3V | SPI | 16Kb | | | | | | | | Count | SOIC14 |
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Top SPI Processor Companion FAQs
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Q:
How long will a backup supercap last after a power loss?
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A:
Using a 1F supercap, the RTC will operate for approximately two weeks.
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Q:
How much time will it take to charge up a supercap?
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A:
A: The FM3130, FM3127x, FM31L27x, and FM33xx have a fast charge mode. If a 1F supercap has been discharged to 1.5V, it will take approximately 30 minutes.
See also: AN404 – RTC Backup and UL
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Q:
Why doesn’t the RTC/oscillator run? Why is the RTC running slow? It seems that I have everything connected properly on my board, however I cannot activate the RTC with the crystal.
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A:
Check that your board layout is clean - do not route switching signals next to the X1/X2 pins and be sure to have a guard-ring around the X1/X2 pins. Typically if the crystal pins are being disturbed by nearby switching signals, you will observe the CAL output is much lower than 512 Hz. Other things to check: be sure to remove solder flux near crystal pins, replace the crystal, initialize all battery-backed registers to a value within its valid range.
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Q:
Why use I2C over SPI, or vice versa?
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A:
Two-wire (I2C) is the most common and many micros implement a two-wire dedicated port. SPI operates at much higher clock rates, up to 16MHz. For simplicity and the use of fewer I/O micro pins, two-wire is generally used.
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I2C Processor Companion
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| Part | Vdd | Interface | Memory | RTC | RTC Alarm | Power Monitor | Watch Dog | Early Power Fail | Serial Number | Battery Switch Over | Event Detect | Package |
| FM31T378 | 2.7-5.5V | I2C | 256Kb | | | | | | | | Count | SOIC14 |
| FM31256 | 2.7-5.5V | I2C | 256Kb | | | | | | | | Count | SOIC14 |
| FM3164 | 2.7-5.5V | I2C | 64Kb | | | | | | | | Count | SOIC14 |
| FM3116 (EOL) | 2.7-5.5V | I2C | 16Kb | | | | | | | | Count | SOIC14 |
| FM3104 (EOL) | 2.7-5.5V | I2C | 4Kb | | | | | | | | Count | SOIC14 |
| FM31L278 | 3V | I2C | 256Kb | | | | | | | | Count | SOIC14 |
| FM31L276 | 3V | I2C | 64Kb | | | | | | | | Count | SOIC14 |
| FM31L274 (EOL) | 3V | I2C | 16Kb | | | | | | | | Count | SOIC14 |
| FM31L272 (EOL) | 3V | I2C | 4Kb | | | | | | | | Count | SOIC14 |
| FM31278 | 5V | I2C | 256Kb | | | | | | | | Count | SOIC14 |
| FM31276 | 5V | I2C | 64Kb | | | | | | | | Count | SOIC14 |
| FM31274 (EOL) | 5V | I2C | 16Kb | | | | | | | | Count | SOIC14 |
| FM31272 (EOL) | 5V | I2C | 4Kb | | | | | | | | Count | SOIC14 |
| FM3130 (EOL) | 3V | I2C | 64Kb | | | | | | | | N/A | SOIC8 or DFN8 |
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Top I2C Processor Companion FAQs
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Q:
A common issue with I2C devices in general (F-RAM included) is that reads are not easily terminated due to microcontroller timing problems, multi-master issues, or a brownout condition. How do I interrupt a pending memory read?
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A:
The microcontroller could issue a STOP condition but this may be difficult since bus contention will occur. If the micro cannot drive SDA high, there is an alternate method. The second way to abort a pending read operation is to issue clocks until a data bit value of ‘1’ occurs. A ‘1’ data bit will cause the serial FRAM to release the SDA line since it only drives low. To make this method work, the master issues an SCL rising edge, then reads the SDA line while SCL is high. If SDA is ‘0’, then another clock must be issued. If SDA is ‘1’, then the master can force SDA low while SCL is high. This is a START condition. A START condition also will cause the memory to end the read operation immediately.
See also: AN201 Interrupting a Two-Wire Read
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Q:
How long will a backup supercap last after a power loss?
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A:
Using a 1F supercap, the RTC will operate for approximately two weeks.
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Q:
How much time will it take to charge up a supercap?
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A:
A: The FM3130, FM3127x, FM31L27x, and FM33xx have a fast charge mode. If a 1F supercap has been discharged to 1.5V, it will take approximately 30 minutes.
See also: AN404 – RTC Backup and UL
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Q:
What is the Ibak current when I insert a battery and Vdd is off?
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A:
When a battery is first attached to the FM31xx while Vdd is powered off, there are a number of registers inside the chip that come up in an unknown state. These circuits are connected to the internal power supply. It is possible that the Ibak current is a few microamps or as much as 100 microamps. It's a random startup condition. Once Vdd is applied, the Ibak current goes to zero. All internal circuits are set to known states. When Vdd is then powered down, the Ibak current is < 1uA. This issue has been resolved on the FM3127x, FM31L27x, FM33xx, FM3130, and FM3135 devices.
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Q:
Why doesn’t the RTC/oscillator run? Why is the RTC running slow? It seems that I have everything connected properly on my board, however I cannot activate the RTC with the crystal.
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A:
Check that your board layout is clean - do not route switching signals next to the X1/X2 pins and be sure to have a guard-ring around the X1/X2 pins. Typically if the crystal pins are being disturbed by nearby switching signals, you will observe the CAL output is much lower than 512 Hz. Other things to check: be sure to remove solder flux near crystal pins, replace the crystal, initialize all battery-backed registers to a value within its valid range.
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Q:
Why use I2C over SPI, or vice versa?
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A:
Two-wire (I2C) is the most common and many micros implement a two-wire dedicated port. SPI operates at much higher clock rates, up to 16MHz. For simplicity and the use of fewer I/O micro pins, two-wire is generally used.
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End-of-Life (EOL) or Not Recommended for New Design (NRND)
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| Part | Vdd | Interface | Memory | RTC | RTC Alarm | Power Monitor | Watch Dog | Early Power Fail | Serial Number | Battery Switch Over | Event Detect | Package |
| FM32L278 (EOL) | 3V | I2C | 256Kb | | | | | | | | Count | SOIC14 |
| FM32L276 (EOL) | 3V | I2C | 64Kb | | | | | | | | Count | SOIC14 |
| FM32L274 (EOL) | 3V | I2C | 16Kb | | | | | | | | Count | SOIC14 |
| FM32L272 (EOL) | 3V | I2C | 4Kb | | | | | | | | Count | SOIC14 |
| FM32278 (EOL) | 5V | I2C | 256Kb | | | | | | | | Count | SOIC14 |
| FM32276 (EOL) | 5V | I2C | 64Kb | | | | | | | | Count | SOIC14 |
| FM32274 (EOL) | 5V | I2C | 16Kb | | | | | | | | Count | SOIC14 |
| FM32272 (EOL) | 5V | I2C | 4Kb | | | | | | | | Count | SOIC14 |
| FM32256 (EOL) | 3-5V | I2C | 256kb | | | | | | | | Count | SOIC14 |
| FM3264 (EOL) | 3-5V | I2C | 64Kb | | | | | | | | Count | SOIC14 |
| FM3216 (EOL) | 3-5V | I2C | 16Kb | | | | | | | | Count | SOIC14 |
| FM3204 (EOL) | 3-5V | I2C | 4Kb | | | | | | | | Count | SOIC14 |
| FM3135 w/Xtal (EOL) | 3V | I2C | 64Kb | | | | | | | | N/A | SOIC20 |
| FM4005 (NRND) | 3-5V | I2C | 0Kb | | | | | | | | Count | SOIC14 |
| FM30C256 (NRND) | 5V | I2C | 256Kb | | | | | | | | N/A | SOIC20 |
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