Hello, this is Bee. In the last issue, we learned about the time it takes for configuration. Previously, we thought that once the power was turned on and the configuration was finished, the FPGA would enter user mode, but it turns out that the circuitry inside the FPGA goes through multiple steps to operate.
In this article, we will study one of them, Power On Reset ( POR ). Power On Reset Time refers to the time between when the power supply stabilizes and when the configuration starts.
In industry jargon, turning on the power is referred to as "fire".
When I first heard it, I thought it meant incinerating the device.
I would like to go through the time it takes for the circuit configured on the FPGA to start operating after the power is turned on.
The FPGA is running through the steps as shown in the figure below.
- Power on
- Power supply stabilizes: Voltage reaches the specified value.
- POR ： Power On Reset
- Configuration
- Initialize
- User mode
Ramp Time ( tRAMP ) is defined as the time from power-on until the power supply stabilizes.
This is the time required for the power supply from the power supply IC (regulator), etc. to reach the specified voltage level from the start of voltage supply.
Power On Reset (POR) is initiated when the power supply is stabilized within the Ramp Time. POR is literally a process of resetting the FPGA before starting configuration. Therefore, the sooner the power supply is stabilized, the sooner POR is initiated and, consequently, the sooner the FPGA can enter user mode.
The POR is described in the following section.
configuration -> Configuration Requirement -> Power On Reset (POR) Ciurcuit
So how are these times determined? I searched for "POR" in the datasheet and got a hit.
Data Sheet -> Recommended Operating Conditions -> tables 1-4 -> Note (7), (8)
Fast mode: approx. tPOR = 3ms to 9ms
Standard mode: approx. tPOR = 50 to 200ms
The Power On Reset time ( tPOR ) also includes tRAMP. I was getting confused while writing the article, so I drew a diagram showing the respective times.
I see that the time from power on to user mode can be expressed by the following equation.
Time to enter user mode = Power On Reset Time + Configuration Time + Initialization Time
Note that tPOR and tRAMP will vary depending on whether Fast Mode or Standard Mode is selected in the configuration mode.
In this AS configuration mode, you can also select Fast or Standard Mode depending on how the MSEL[2..0] pin is processed.
The previously calculated configuration time is 147.2 ms in the worst case, so adding the tPOR time, the calculation is as follows.
(Click here for more information on configuration time )
POR + configuration time = 200 ms + 147.2 ms = 346.2 ms
If you add the initialization time, you will get the time from power-on to user mode.
We will study the initialization time in the next issue.
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