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

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 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

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.

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. (?)