Sign in
Search hc11
Subscribe to hc11
Ads
Discussion Groups
Discussion Groups | M68HC11 | Source and Sink max
Technical discussions about Freescale Microcontrollers: M68HC11. (Freescale Semiconductor is a Subsidiary of Motorola).
Source and Sink max - Jim Dodd - Feb 11 9:36:00 2005
|
I'm using the 68HC11F1. For years I've been assuming that the current source and sink maximums for the Port A lines (and sink for the Port B digital input only lines) were the same as other TTL or HCMOS parts but now I read in the famous 68HC11 Reference manual that these values are really 25 mA (and can actually handle up to 100 mA). Can that be correct? I'm updating our manual and need to include this information. I actually did a crude test of this on our board and it seems to still be working. Thanks for any help, Jim Dodd Onset Computer Corp. __________________________________ |
|
|
(You need to be a member of hc11 -- send a blank email to hc11-subscribe@yahoogroups.com )
RE: Source and Sink max - Redd, Emmett R - Feb 11 9:41:00 2005
|
While I don't have the book in front of me, I remember it saying you also have to consider the total power dissipated by the package. Therefore, you cannot simultaneously sink 25 mA by more than just a few pins. Emmett Redd Ph.D. mailto: Associate Professor (417)836-5221 Department of Physics, Astronomy, and Materials Science Southwest Missouri State University Fax (417)836-6226 901 SOUTH NATIONAL Dept (417)836-5131 SPRINGFIELD, MO 65804 USA > -----Original Message----- > From: Jim Dodd [mailto:] > Sent: Friday, February 11, 2005 7:36 AM > To: > Subject: [m68HC11] Source and Sink max > I'm using the 68HC11F1. For years I've been assuming that the > current source > and sink maximums for the Port A lines (and sink for the Port > B digital input > only lines) were the same as other TTL or HCMOS parts but now > I read in the > famous 68HC11 Reference manual that these values are really > 25 mA (and can > actually handle up to 100 mA). Can that be correct? I'm > updating our manual and > need to include this information. > > I actually did a crude test of this on our board and it seems > to still be > working. > > Thanks for any help, > > Jim Dodd > Onset Computer Corp. > > > __________________________________ > > Yahoo! Groups Links |
(You need to be a member of hc11 -- send a blank email to hc11-subscribe@yahoogroups.com )
Re: Source and Sink max - Bob Smith - Feb 11 10:43:00 2005
|
Jim -- Over the years working with various members of the Motorola MCU family of devices, I have found that the current handling capability of output port pins varies quite a bit from device to device and also between individual members with in families. For example, you have found ratings to 25ma for F! devices, but my E seriesTech Data manual makes it pretty clear that Vo(hi) (sourcing) is rated at -0.8ma while Vout(lo) (sinking) is rated at 1.6ma for all output pins with few exceptions such as XTAL. For the 'HC11 family devices the definitive "Electrical Characteristics" for each series is found in the "Technical Data Manual" for each series, not in the "Pink/White" books. I have also found that some port pins are symetrical, i.e. Source and Sink ratings are the same, while others are not. It is also true that some ports of a given device are rated to drive heavier loads than others. My "rule of thumb" for this aspect of design considerations is that "there ain't no rule of thumb". You have to find the "Electrical Characteristics" table for each device you are working with and then check each pin(port) within that device. That having been said, I generally regard Vsat at the most important characteristic to observe when checking port function. You should then calculate the port pin dissapation pin by pin and also watch the overall dissapation on the device. Certain port pins may also have AC timing considerations such as rise/fall times which should be observed. Note that if you do decide to overdrive any port pin you become responsible for 100% testing that pin to assure that you do not run into a "weak sister" part that meets factory specs but doesn't handle your heaver load well. Bob Smith --- Avoid computer viruses, Practice safe hex --- -- Specializing in small, cost effective embedded control systems -- http://www.smithmachineworks.com/embedprod.html Robert L. (Bob) Smith Smith Machine Works, Inc. 9900 Lumlay Road Richmond, VA 23236 804/745-2608 ----- Original Message ----- From: "Jim Dodd" <> To: <> Sent: Friday, February 11, 2005 8:36 AM Subject: [m68HC11] Source and Sink max > I'm using the 68HC11F1. For years I've been assuming that the current source > and sink maximums for the Port A lines (and sink for the Port B digital input > only lines) were the same as other TTL or HCMOS parts but now I read in the > famous 68HC11 Reference manual that these values are really 25 mA (and can > actually handle up to 100 mA). Can that be correct? I'm updating our manual and > need to include this information. > > I actually did a crude test of this on our board and it seems to still be > working. > > Thanks for any help, > > Jim Dodd > Onset Computer Corp. > > > __________________________________ > > Yahoo! Groups Sponsor > ADVERTISEMENT > -------------------------------------------------------------------------- ------ > Yahoo! Groups Links > > a.. To |
(You need to be a member of hc11 -- send a blank email to hc11-subscribe@yahoogroups.com )
Re: Source and Sink max - Mark Schultz - Feb 12 15:05:00 2005
|
--- In , "Bob Smith" <bobsmith5@v...> wrote: > My "rule of thumb" for this aspect of design considerations is that > "there ain't no rule of thumb". You have to find the "Electrical > Characteristics" table for each device you are working with and then > check each pin(port) within that device. For the most part, I agree with what Bob has said on this subject. My personal "rule of thumb" (which is really not inconsistent with Bob's lack of one ;) is to assume that any I/O pin that is not specifically touted by the mfr. to be capable of source/sinking high current loads requires some sort of external drive device/circuit. There are some microcontrollers I have encountered that provide one or more output pins that are specifically rated to drive low-medium current loads such as LEDs, or provide drive characteristics consistent with the requirements for certain bus specifications (e.g. I2C). For such pins, I regard it as 'acceptable design practice' to drive loads such as LEDs directly, assuming of course that I stay within the mfr's specifications for such 'special' outputs. In all other cases, I assume that the output in question is strictly intended to drive "logic only" loads. I typically use devices such as the readily available (and inexpensive) ULN2003/MC1413 or ULN2803; these devices accept TTL/CMOS (5V) "logic levels" as inputs and provide a current-sink output good for around 100mA (more or less, depending on total device power dissipation). Such devices are great for driving LEDs, relays, and the like. Small-signal NPN transistors such as the 2N2222 or 2N3904 in conjunction with an appropriate base current limiting resistor (I usually use 1K - 10K) can also be used. Small-signal N-channel logic-level MOSFETs (2N7000 ?) also work well, and (usually) do not require a gate current-limiting resistor. You have to be careful with MOSFETS tho if you are switching them at high frequency; the gate is capacitive, which means that effective power dissipation on the pin driving it will be a function of switching frequency. Also, the MOSFET itself will have a tendency to operate for part of its switching interval in the "linear region" (e.g. acts as a variable resistor) when driven by a high-impedance (weak/low drive current) source. This is usually not a problem when driving indicator LEDs, but could potentially be a problem if you were, for example, switching a high-current IR LED at IR-remote frequencies (~ 38 KHz). |
(You need to be a member of hc11 -- send a blank email to hc11-subscribe@yahoogroups.com )