I want to extend my mini2440 with two additional rs232 ports. On the connectors on the mini2440 there are txd,rxd,gnd and 5V. Is the rxd pin 5v tolerant, so that I can use a normal max232 at these 4 pins? or is it necessery to use the 3.3V Version max3232 and take the supply from any other 3.3V pin?
The 5v regular max232 will work
Have a look in the first datasheet on the Downloads page.
In the datasheet the level-converter is supplied with 3.3V. thats perfectly clear. This will work, no question. But I wanted to know if I can use a normal max232 and give it a 5V powersupply, because the pinout on the connector on the board has a 5V pin. But when I do this, I would get 5V output of the max232 on the rxd-Line. This is connected to our processor. So is the processor input capable of this 5V input-signal? Or would I damage the processor?
Section 27 and table 27-1 in the datasheet says:
DC Input Voltage VIN 3.3V Input buffer 4.8V
3.3V Interface / 5V Tolerant input buffer 6.5V
Now, does this refer to I/O? Vin is mentioned again in table 27.3 as being
related to I/O.
The word tolerant only shows up in one other place on page 1-19.
I'll check with the guys actually using this part tomorrow. I sounds like
it is 5V tolerant, but you DO want to be sure.
Dave
what level converter are you talking about? On the PCB?
Yes I should be sure before connecting ;-)
The level converter on the pcb is operated with 3.3V, so there is no
problem.
I am talking about my own level converter:
I want to use the second and third serial port.
On the pcb are three connectors with tzhe following pin out:
1 TXD1
2 RXD1
3 VDD5V
4 GND
I want to do the following:
Can I supply the max233 with 5V?
The problem will be that the RX -Input needs to be tolerant to 5V.
_________
1 TXD1 ------------------------| |------------ RS232 level
2 RXD1 ------------------------| MAX |------------
| 233 |
| or |
3 VDD5V -----------------------| MAX |
4 GND -----------------------| 232 |
|_______|
or do I have to use:
_________
1 TXD1 ------------------------| |------------ RS232 level
2 RXD1 ------------------------| MAX |------------
| 3233 |
| or |
3.3V from somewhere else-| MAX |
4 GND -----------------------| 3232 |
|_______|
thanks a lot
That datasheet I am referring to is the datasheet for the S3C2440. The other thing you need to consider is will a MAX233 input work properly with the logic high and logic low levels from an I/O port on the S3C2440. Interfacing SPI on a 5V uP to SD cards usually have level translators to ensure proper operation. It may work OK. Off to work and I'll get back to you with I/O voltage levels. Dave
I only have the S3C2410A manual in front of me, but you should be able to find the same information in the datasheet for the S3C2440. Somewhere around page 1-19 or before that, there is a listing of the I/O pins with a column at the end showing what TYPE it is. Evidently, T6 are 5V tolerant pins. You need to look through the list and confirm that the pins used for your application are of this type. In the S3C2410 manual we found that the SPI pins are 5V tolerant. Hope this helps. Dave
It´s work with 5 Vdc or you burn the RX pin ? Reading the datasheet, i undestand thats its will be 5Vdc Tolerant... "Table 27-2. Recommended Operating Conditions.... DC input voltage VIN 3.3V Input buffer – 0.3 VDDOP+0.3 3.3V Interface / 5V Tolerant input buffer – 0.3 5.25" I like to interface it to a 5 Vdc Pic microcontroller.... Best regards, Arnaldo Yamaoka.
Hm, ok, so I looked into the data sheet. They are marked as t8. at the entry for t8 it is not mentioned that they are 5 V tolerant. So I decided not to try it. I will have to configure a 3.3V interface. thanks anyway.
I guess the 5V is so people can connect an external 5V to 3V3 converter. Seems odd as there is a 3V3 regulator on the PCB, why not just bring that out? Another option, which I am not recommending, is use two resistors on the MAX232 RXD line . . . a 2K2 in series and a 3K3 to ground. This would reduce the 5v to under 3V3. You would still have to ensure that a HI on the S3C2440 I/O port is above the logic high requirement for the MAX232 TXD port. Go with a separate 3V3 LDO regulator.
It depends more on speed (baudrate) but a 1.8K + 3.3K voltage divider, can do the job... the max232 input can work with 3.3v but note that it will pull-up with 40uA (or less) i don't think it will be an issue... another way is using a 1k res + 3.3v Zener as a Divider... of course there are more fancy (and reliable) options, but this can work well on this board