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Hack a datalogger into existing design

Started by mpm April 11, 2020
Pretty sure the answer is "Yes", but let me ask it anyway....

Situation:
Need to add a datalogger to an existing design, but there are no free ports left on the microcontroller.

The microcontroller is an AT89LP51ED2.  (An 8-bit, 8051 variant)
Port-0 outputs data ONLY to (3) D-Type transparent octal latches (74ACT573N), which are individually latched via some pins on Port-2 of the microcontroller.

The latches are written infrequently, and are never left un-latched in normal operation (i.e., we don't use the "transparent" feature of this part).

So.... 

Can I use a couple of Port-0 port pins for I2C SDA & SCL lines to connect up some parts to make a datalogger?  (I'm thinking a 24C32 for the memory, and DS3231 for the RTC.)

It seems to me that as long as the 573 latches are latched with the intended data, I can then do whatever I want with the Port-0 pins (such as service a RTC & Memory datalogger).

All the voltages are OK  (+5 VDC is used everywhere in this particular product).

So other than adjusting the code, is there anything I'm missing?

Thanks for looking / confirming this will work. (?)
On 4/11/20 9:22 AM, mpm wrote:
> Pretty sure the answer is "Yes", but let me ask it anyway.... > > Situation: > Need to add a datalogger to an existing design, but there are no free ports left on the microcontroller. > > The microcontroller is an AT89LP51ED2. (An 8-bit, 8051 variant) > Port-0 outputs data ONLY to (3) D-Type transparent octal latches (74ACT573N), which are individually latched via some pins on Port-2 of the microcontroller. > > The latches are written infrequently, and are never left un-latched in normal operation (i.e., we don't use the "transparent" feature of this part). > > So.... > > Can I use a couple of Port-0 port pins for I2C SDA & SCL lines to connect up some parts to make a datalogger? (I'm thinking a 24C32 for the memory, and DS3231 for the RTC.) > > It seems to me that as long as the 573 latches are latched with the intended data, I can then do whatever I want with the Port-0 pins (such as service a RTC & Memory datalogger). > > All the voltages are OK (+5 VDC is used everywhere in this particular product). > > So other than adjusting the code, is there anything I'm missing? > > Thanks for looking / confirming this will work. (?) >
You need some way to make sure writing data to the latches doesn't mess up your SDA & SCL lines.
On 2020-04-11 10:22, mpm wrote:
> Pretty sure the answer is "Yes", but let me ask it anyway.... > > Situation: > Need to add a datalogger to an existing design, but there are no free ports left on the microcontroller. > > The microcontroller is an AT89LP51ED2. (An 8-bit, 8051 variant) > Port-0 outputs data ONLY to (3) D-Type transparent octal latches (74ACT573N), which are individually latched via some pins on Port-2 of the microcontroller. > > The latches are written infrequently, and are never left un-latched in normal operation (i.e., we don't use the "transparent" feature of this part). > > So.... > > Can I use a couple of Port-0 port pins for I2C SDA & SCL lines to connect up some parts to make a datalogger? (I'm thinking a 24C32 for the memory, and DS3231 for the RTC.) > > It seems to me that as long as the 573 latches are latched with the intended data, I can then do whatever I want with the Port-0 pins (such as service a RTC & Memory datalogger). > > All the voltages are OK (+5 VDC is used everywhere in this particular product). > > So other than adjusting the code, is there anything I'm missing? > > Thanks for looking / confirming this will work. (?) >
Another approach would be to replace the 573 with a 595, which would free up 5 pins. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
lørdag den 11. april 2020 kl. 17.39.31 UTC+2 skrev Phil Hobbs:
> On 2020-04-11 10:22, mpm wrote: > > Pretty sure the answer is "Yes", but let me ask it anyway.... > > > > Situation: > > Need to add a datalogger to an existing design, but there are no free ports left on the microcontroller. > > > > The microcontroller is an AT89LP51ED2. (An 8-bit, 8051 variant) > > Port-0 outputs data ONLY to (3) D-Type transparent octal latches (74ACT573N), which are individually latched via some pins on Port-2 of the microcontroller. > > > > The latches are written infrequently, and are never left un-latched in normal operation (i.e., we don't use the "transparent" feature of this part). > > > > So.... > > > > Can I use a couple of Port-0 port pins for I2C SDA & SCL lines to connect up some parts to make a datalogger? (I'm thinking a 24C32 for the memory, and DS3231 for the RTC.) > > > > It seems to me that as long as the 573 latches are latched with the intended data, I can then do whatever I want with the Port-0 pins (such as service a RTC & Memory datalogger). > > > > All the voltages are OK (+5 VDC is used everywhere in this particular product). > > > > So other than adjusting the code, is there anything I'm missing? > > > > Thanks for looking / confirming this will work. (?) > > > > Another approach would be to replace the 573 with a 595, which would > free up 5 pins. >
it would free even more, only three pins needed to drive a string of shift registers, instead of the 8data + 3latch
On 2020-04-11 11:52, Lasse Langwadt Christensen wrote:
> lørdag den 11. april 2020 kl. 17.39.31 UTC+2 skrev Phil Hobbs: >> On 2020-04-11 10:22, mpm wrote: >>> Pretty sure the answer is "Yes", but let me ask it anyway.... >>> >>> Situation: Need to add a datalogger to an existing design, but >>> there are no free ports left on the microcontroller. >>> >>> The microcontroller is an AT89LP51ED2. (An 8-bit, 8051 variant) >>> Port-0 outputs data ONLY to (3) D-Type transparent octal latches >>> (74ACT573N), which are individually latched via some pins on >>> Port-2 of the microcontroller. >>> >>> The latches are written infrequently, and are never left >>> un-latched in normal operation (i.e., we don't use the >>> "transparent" feature of this part). >>> >>> So.... >>> >>> Can I use a couple of Port-0 port pins for I2C SDA & SCL lines to >>> connect up some parts to make a datalogger? (I'm thinking a >>> 24C32 for the memory, and DS3231 for the RTC.) >>> >>> It seems to me that as long as the 573 latches are latched with >>> the intended data, I can then do whatever I want with the Port-0 >>> pins (such as service a RTC & Memory datalogger). >>> >>> All the voltages are OK (+5 VDC is used everywhere in this >>> particular product). >>> >>> So other than adjusting the code, is there anything I'm missing? >>> >>> Thanks for looking / confirming this will work. (?) >>> >> >> Another approach would be to replace the 573 with a 595, which >> would free up 5 pins. >> > > it would free even more, only three pins needed to drive a string of > shift registers, instead of the 8data + 3latch
Five pins, for large values of five. ;) Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com