LeafLabs Garden » Topic: How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?

LeafLabs Garden » Topic: How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port? http://forums.leaflabs.com/topic.php?id=240 A place to share, learn, and grow... en-US Fri, 22 Jan 2016 00:12:39 +0000 http://bbpress.org/?v=1.0.2 <![CDATA[Search]]> q http://forums.leaflabs.com/search.php gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240&page=2#post-1764 Tue, 12 Oct 2010 04:50:59 +0000 gbulmer 1764@http://forums.leaflabs.com/ llandy - Sorry, I was trying to be as accurate as I know how (apologies for my 2.5 vs 2.25 gaff) I always learn something from these discussions, partly because I have to reexamine my old assumptions, so I am grateful for your forbearance, putting up with me being pernickety. I think we nailed this one :-) Aside - I don't think most OS's could cope with 2.25mbps, with a traditional serial interface. I hadn't thought about the implications until now, but I wonder if maybe that's why USB was designed to pole the devices; to make the interface electronics cheap on the host side? leaflabsandy on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1761 Mon, 11 Oct 2010 23:08:10 +0000 leaflabsandy 1761@http://forums.leaflabs.com/ Summary is 100% correct. BTW ... That is twice in 2 weeks that you got teflon llandy. gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1760 Mon, 11 Oct 2010 22:53:00 +0000 gbulmer 1760@http://forums.leaflabs.com/ Okay, so you have read the code, and you are now agreeing with my intial Summary? <blockquote>There are other details to consider, but I think the important points are: 1. Baud ~= Bits/second in this case of USARTs 2. 2.25Megabaud and 4.5Megabaud are close enough to correct, and 'The max baud on comm. 2 & 3 is 250K and on comm 1 450K' is 10x too small. </blockquote> ('Night all) gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1759 Mon, 11 Oct 2010 22:51:02 +0000 gbulmer 1759@http://forums.leaflabs.com/ llandy - sorry, my post, and your edits crossed again. I understand where they come from, those values are the underlying clock rates. I'm not sure what the "new summary" needs to say. I think I wrote it in my first summary. leaflabsandy on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1758 Mon, 11 Oct 2010 22:48:16 +0000 leaflabsandy 1758@http://forums.leaflabs.com/ Code does not lie. gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1757 Mon, 11 Oct 2010 22:41:28 +0000 gbulmer 1757@http://forums.leaflabs.com/ Okay, so according to the code usart_num=USART1, max_baud=4500000UL = 4,500,000 = 4.5Mbaud usart_num=USART2, max_baud=2250000UL = 2,250,000 = 2.25Mbaud usart_num=USART3, max_baud=2250000UL = 2,250,000 = 2.25Mbaud not 450kbaud, or 250/225kbaud. Agreed? leaflabsandy on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1755 Mon, 11 Oct 2010 22:33:11 +0000 leaflabsandy 1755@http://forums.leaflabs.com/ From HardwareSerial.cpp: IDE 0.0.7 HardwareSerial Serial1(USART1, 4500000UL, GPIOA_BASE, 9, 10, TIMER1, 2); HardwareSerial Serial2(USART2, 2250000UL, GPIOA_BASE, 2, 3, TIMER2, 3); HardwareSerial Serial3(USART3, 2250000UL, GPIOB_BASE, 10, 11, 0, 0); // TODO: High density device ports HardwareSerial::HardwareSerial(uint8 usart_num, uint32 max_baud, GPIO_Port *gpio_port, uint8 tx_pin, uint8 rx_pin, uint8 timer_num, uint8 compare_num) { this->usart_num = usart_num; this->max_baud = max_baud; this->gpio_port = gpio_port; this->tx_pin = tx_pin; this->rx_pin = rx_pin; this->timer_num = timer_num; this->compare_num = compare_num; ----------------------------------------------------------------------- "Never believe a person for what they say but what they do" ----------------------------------------------------------------------- It seems that in the above core code 4500000 & 2250000 are the bauds? Gbulmer ... a new summary is needed. gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1754 Mon, 11 Oct 2010 22:10:11 +0000 gbulmer 1754@http://forums.leaflabs.com/ llandy - your edits crossed with my previous response again. <blockquote>The above 5 & 6 statements are wrong. He computed the baud rate wrong by 10 </blockquote> No. No worse than by a factor of (8/10). Baud is a measure of the number of distinct symbols changes on the line/second (4.5MHz = 4,500,000 symbol changes in the fastest case, 2.25MHz otherwise), and the number of symbols, which for a USART is 2 (it is not a multi-tone modem). I was taught to subtract the protocol framing (2 bits in your example) to avoid misleading folks. <blockquote>So Perry H inferred 225000 is the baud rate which is the same as 225 KBaud which is the same as 2.25 Mbit/s. </blockquote> Well, a baud rate of 225000 baud is 225KBaud (ignoring framing, which I think we agree can be excluded from the measurment of transmitted information), but I'd have to wait for Perry to explain what he was inferring, it is not the same as 2.25Mbit/s. gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1753 Mon, 11 Oct 2010 22:02:19 +0000 gbulmer 1753@http://forums.leaflabs.com/ <blockquote>10 is the frame # of bits 8 N 1 </blockquote> I exactly agree that the protocol frame (start, stop(s) and parity), are not part of the information transmission. That's what I was hinting at when I wrote <blockquote>(actually, I was taught it still isn't, but that is looking at small details). </blockquote> In this case, I read that as 8 data bits, no-parity, 1 stop bit (there is always 1 start bit), so for every 10 bits signalled on the 'transmission medium', there are 8 bits of data. So, I am very happy to derate the 4.5Mbps to 4,500,000 *(8/10) = 3.6Mbaud and similarly the 2.25mbps to 2Mbaud. leaflabsandy on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1752 Mon, 11 Oct 2010 21:42:01 +0000 leaflabsandy 1752@http://forums.leaflabs.com/ Quote: "So how would you calculate the baud rate for the STM32F 2.25Mbits and 4.5Mbits USARTs, and what values do you get?" Reply: Again, from above: 4.5Mb/s = 4500000/10 = 450KBaud <10 is the frame # of bits 8 N 1> 2.25Mb/s = 2250000/10 = 225KBaud Quote: "There are other details to consider, but I think the important points are: 1. Baud ~= Bits/second in this case of USARTs 2. 2.25Megabaud and 4.5Megabaud are close enough to correct, and 'The max baud on comm. 2 & 3 is 250K and on comm 1 450K' is 10x too small." Reply: Sorry, I totally disagree with 1 & 2 From the link: <a href="http://forums.leaflabs.com/topic.php?id=83" rel="nofollow">http://forums.leaflabs.com/topic.php?id=83</a> Perry H Quote: "4. You can set any rate up to the max of the uart. They aren't required to be fixed, the clock divisors are computed from the entered baud rate. You listed many common rates above. At the moment (as Bryan noted), they're limited to 225000, which is a bug that I didn't catch. There's a fix coming soon." So Perry H inferred 225000 is the baud rate which is the same as 225 KBaud which is the same as 2.25 Mbit/s. He goes on to say "Error checking is performed, you can't set a baud rate higher than the max baud rate." 5. USART1 tops out at 4.5Mbits/s = 4500000 baud 6. USART2 and USART3 are clocked from the slower APB1 bus, so they top out at 2.5Mbits/s = 2250000 baud. -------------------------------------------------------------------------------------- The above 5 & 6 statements are wrong. He computed the baud rate wrong by 10 Edit: Note: Both of Perry's statements contradict each other. gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1751 Mon, 11 Oct 2010 21:39:01 +0000 gbulmer 1751@http://forums.leaflabs.com/ llandy 4.5Mbps = 4.5 megabits/second (Mbps) = 4,500,000 bits/second = 4,500,000 Baud = 4.5Mbaud on a USART (a system with only two symbols/unit transission time) gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1750 Mon, 11 Oct 2010 21:32:45 +0000 gbulmer 1750@http://forums.leaflabs.com/ llandy - I was following the convention you adopted in your post <blockquote>Also, ONLY Comm #2 and Comm #3 have hardware handshake lines! (RTS,CTS) - See GPIO docs. The max baud on comm. 2 & 3 is 250K and on comm 1 450K <-------- </blockquote> <blockquote>Reply: STMf130RB.PDF Section 2.3.17 Quote: Universal synchronous/asynchronous receiver transmitter (USART) One of the USART interfaces is able to communicate at speeds of up to 4.5 Mbit/s. The other available interfaces communicate at up to 2.25 Mbit/s. <----- </blockquote> Yes, that's where I got the figures from. I apologise for my transcription error, I wrote 2.5Megabaud, rather than 2.25Megabaud. I was probably reading your post where you wrote <blockquote>max baud on comm. 2 & 3 is 250K </blockquote> 2.5Megabaud and 4.5megabaud, are 10x faster than <blockquote>max baud on comm. 2 & 3 is 250K and on comm 1 450K </blockquote> which seemed to be the important point for StephenFromNYC, who is asking using a USART to move data at high speed. It kinda doesn't matter whether we are using bits/second (as used by ST) or baud, because close enough in this particular case. <blockquote>baud'' and`bps'' are perhaps one of the most misused terms in the computing and telecommunications field. Many people use these terms interchangeably, when in fact they are not! </blockquote> Strongly agree. Baud rate is not <blockquote>The baud rate is a measure of how many times per second a signal changes (or could change). </blockquote> So how would you calculate the baud rate for the STM32F 2.25Mbits and 4.5Mbits USARTs, and what values do you get? Actually, I dont believe that is correct. Wikipedia has the definition which I was taught, <a href="http://en.wikipedia.org/wiki/Baud">Baud</a>: <blockquote>In telecommunications and electronics, baud (pronounced /ˈbɔːd/, unit symbol "Bd") is synonymous to symbols per second or pulses per second. It is the unit of symbol rate, also known as baud rate or modulation rate; the number of distinct symbol changes (signaling events) made to the transmission medium per second in a digitally modulated signal </blockquote> My emphasis on symbols. <blockquote>The term baud rate has sometimes incorrectly been used to mean bit rate, since these rates are the same in old modems as well as in the simplest digital communication links using only one bit per symbol, such that binary "0" is represented by one symbol, and binary "1" by another symbol. In more advanced modems and data transmission techniques, a symbol may have more than two states, so it may represent more than one bit (a bit (binary digit) always represents one of exactly two states). </blockquote> So the difference between Baud and bps matters a lot on a system which can have more than two symbols on the line, but when there are only two symbols, voltage high and low, as on a STM32F USART, I believe it is close enough to be treated as equivalent (actually, I was taught it still isn't, but that is looking at small details). There are other details to consider, but I think the important points are: 1. Baud ~= Bits/second in this case of USARTs 2. 2.25Megabaud and 4.5Megabaud are close enough to correct, and 'The max baud on comm. 2 & 3 is 250K and on comm 1 450K' is 10x too small. leaflabsandy on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1749 Mon, 11 Oct 2010 20:18:02 +0000 leaflabsandy 1749@http://forums.leaflabs.com/ Quote: "StephenFromNYC - The max baud rates on the USARTS are 4.5Megabaud, and 2.5Megabaud, not 250k baud or 450k baud" Reply: STMf130RB.PDF Section 2.3.17 Quote: Universal synchronous/asynchronous receiver transmitter (USART) One of the USART interfaces is able to communicate at speeds of up to 4.5 Mbit/s. The other available interfaces communicate at up to 2.25 Mbit/s. <----- Is there a difference between "Mega bits per second" and baud rate? <code>baud'' and</code>`bps'' are perhaps one of the most misused terms in the computing and telecommunications field. Many people use these terms interchangeably, when in fact they are not! bps is simply the number of bits transmitted per second. The baud rate is a measure of how many times per second a signal changes (or could change). <a href="http://www.sengpielaudio.com/calculator-transferrate.htm" rel="nofollow">http://www.sengpielaudio.com/calculator-transferrate.htm</a> <a href="http://web.forret.com/tools/bandwidth.asp?speed=4500000&unit=bps" rel="nofollow">http://web.forret.com/tools/bandwidth.asp?speed=4500000&unit=bps</a> 4.5Mb/s = 4500000/10 = 450KBaud 2.25Mb/s = 2250000/10 = 225KBaud <--- whoops? <a href="http://forums.leaflabs.com/topic.php?id=83" rel="nofollow">http://forums.leaflabs.com/topic.php?id=83</a> gbulmer on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1748 Mon, 11 Oct 2010 19:54:30 +0000 gbulmer 1748@http://forums.leaflabs.com/ StephenFromNYC - The max baud rates on the USARTS are 4.5Megabaud, and 2.5Megabaud, not 250k baud or 450k baud. The COM port on your PC might not be able to match 2.5Mbaud; it is worth checking. Even if the port could do it, the OS might not be able to handle it. Yes, you very would likely need a level translater if you want to talk to the COM port on your PC. *Real* RS232 voltage limits are as big as +/-15V. There are several companies which make parts for the job. Maxim is well known: <a href="http://www.maxim-ic.com/datasheet/index.mvp/id/1798">http://www.maxim-ic.com/datasheet/index.mvp/id/1798</a> Once you find where these are catalogued on your favourite electronics supplier, you'll likely find dozens of alternatives. I belive that Maple Native is still an STM32F103/105, and hence is only a full-speed (12Mbits max) USB device. It is not a USB High-speed device. FTDI say the FT232RL (the chip on the Sparkfun and modern devices boards) maximum baud rate is 3Megabaud: <a href="http://www.ftdichip.com/Products/ICs/FT232R.htm">http://www.ftdichip.com/Products/ICs/FT232R.htm</a> I don't know how fast the Maple transfers data (maybe I'll have a bit experiment later in the week), but it is theoretically capable of going faster than that. A feasible option for a much higher transfer speed would be a USB High-speed adapter based on e.g. <a href="http://www.ftdichip.com/Products/ICs/FT2232H.htm">FT2232H</a> The spec says: <blockquote># USB to parallel FIFO transfer data rate up to 10Mbyte/sec (>80Megabaud) # Single channel synchronous FIFO mode for transfers > 25 Mbytes/sec (>200Megabaud)</blockquote> To talk to the FTDI USB chip at these rates, the Maple would be pushing a whole byte at a time into it (based on a brief skim of the datasheet). How fast do you need to move data? leaflabsandy on "How to connect Maple Serial1 pins (RX and TX) to a 9 pin COM port?" http://forums.leaflabs.com/topic.php?id=240#post-1745 Mon, 11 Oct 2010 16:40:42 +0000 leaflabsandy 1745@http://forums.leaflabs.com/ You need a 3.3 VDC TTL to USB converter. Also, you could use the old TTL to RS232 converters but the USB with mini connector is better. There are really two good ones. One is from Sparkfun and the other from Modern Device. (Modern Device is closer to you and I used this one for flash downloading the bootloader) Sparkfun link: <a href="http://www.sparkfun.com/commerce/product_info.php?products_id=10009" rel="nofollow">http://www.sparkfun.com/commerce/product_info.php?products_id=10009</a> Modern Device link: <a href="http://www.moderndevice.com/products/usb-bub" rel="nofollow">http://www.moderndevice.com/products/usb-bub</a> On my Modern device 'BUB' I put two series resistors on the tx and rx lines for current limiting. (300-330 ohm). So you need 3 lines, tx,rx and ground. The BUB tx goes to Maple's rx and BUB rx to Maple's tx and ground to ground. Make sure you set the 3.3VDC jumper on the BUB board!!!! As for handshaking it might be a little more complex because both vendors have the signals for them but you need to do so hacking? Also, you probably need to provide the RTS & CTS signals from Comm x to the BUB board. Also, ONLY Comm #2 and Comm #3 have hardware handshake lines! (RTS,CTS) - See GPIO docs. The max baud on comm. 2 & 3 is 250K and on comm 1 450K <-------- If you really need the "high speed" comm #1 with handshaking you can use software NaK,ACK handshaking. You need to write your own driver. Check with both vendors for the handshaking lines. Note: Even though THe Maple's has hardware handshake lines for Comm #2 & #3 the question arises how do you enable them so the USART can use them? Leaflabs can help you on this.