FYI, it does appear that there is a 12mhz signal on pin 4. It isn't a square wave though. It looks more like a rounded triangle wave.
Are you using the scope probe at 1x or 10x position?
Also, have you verifyed that RST (pin1) is steady near GND level? It would only go high (>3.5V) during the short time the 10uF cap is charging, aka, reseting the Cpu.
Which is better? The erco board is cuter and the software more developed. But the DB board is sharp-looking, roomy, and likely an excellent educational tool for an interested niece or nephew. The educational value may not stop there...The 2051 begs to be reprogrammed and have greater functionality added.
If you reprogram, the AT89C2051 needs 12V, or there are AT89LP2052, AT89LP4052 parts that are 5V SPI programmed.
Addit: I see a ZIF programmer on eBay SP200SE for sub $10
For new designs, these days you would use a newer 51 variant like N76E003/N76E616 for wide Vcc, or EFM8UB1/2/3 for USB. STC8F is also interesting.
A clever paisano of yours, recognizing that the 2051 used a simple protocol (not like the SX!), made his own 2051 burner with an Arduino. I like that idea a lot. Except I'd use a Propeller.
The Keil evaluation assembler isn't all that big (a 77MB download) but has too many conditions that render it unsuitable for the 2051. Fortunately there are competent and free 8051 assemblers. Think that's the direction I'll take today - a free assembler and a diy P1-based chip burner. The 12V business is no problem at all.
Edit: On second thought, the AT89C2051 and its Nuvoton equivalent just aren't worth the effort. Twelve clocks per cycle and an old fuddy-duddy architecture...the nut didn't fall far from the tree on this one! You can spend the same $1.40 for a slightly less-old PIC that will run rings around them.
FYI, it does appear that there is a 12mhz signal on pin 4. It isn't a square wave though. It looks more like a rounded triangle wave.
Are you using the scope probe at 1x or 10x position?
Also, have you verifyed that RST (pin1) is steady near GND level? It would only go high (>3.5V) during the short time the 10uF cap is charging, aka, reseting the Cpu.
FYI, it does appear that there is a 12mhz signal on pin 4. It isn't a square wave though. It looks more like a rounded triangle wave.
Are you using the scope probe at 1x or 10x position?
Also, have you verifyed that RST (pin1) is steady near GND level? It would only go high (>3.5V) during the short time the 10uF cap is charging, aka, reseting the Cpu.
Yes, RST is near GND level. Is it safe for me to directly connect RST to 5V to manually reset the MCU? That way I can eliminate any problems with the reset circuitry by bypassing it.
What's the transistor do?
Some transistors have different pinouts. Could that be the cause?
Is there a link to the schematic?
The transistor drives the speaker. I don't have a schematic for this particular board although it is similar to other boards mentioned in this thread but it contains an additional circuit with a couple of diodes and a resistor connected to some unused connection points labeled +3V and GND. I don't know the purpose of this additional power input (or maybe output).
Is it safe for me to directly connect RST to 5V to manually reset the MCU?
Yes, you could also time the flash with the scope ?
That PCB looks to shunt the resistor-fed LEDs to ground, so both A & K lines pull down.
To pull down, the MCU needs to at least start running. At reset, all pins are lightly hi = LEDS off.
Is it safe for me to directly connect RST to 5V to manually reset the MCU?
Yes, you could also time the flash with the scope ?
That PCB looks to shunt the resistor-fed LEDs to ground, so both A & K lines pull down.
To pull down, the MCU needs to at least start running. At reset, all pins are lightly hi = LEDS off.
I tried connecting pin 1 to pin 20 to force a reset. That still didn't start the clock. I'm beginning to wonder if the MCU isn't programmed with the clock code.
I tried connecting pin 1 to pin 20 to force a reset. That still didn't start the clock. I'm beginning to wonder if the MCU isn't programmed with the clock code.
When does it flash, and for how long ?
I think RST=H is leds off, and RST release -> leds on, means some code is running. Possibly serious supply droop crashes the MCU ?
I tried connecting pin 1 to pin 20 to force a reset. That still didn't start the clock. I'm beginning to wonder if the MCU isn't programmed with the clock code.
When does it flash, and for how long ?
I think RST=H is leds off, and leds on, means some code is running. Possibly serious supply droop crashes the MCU ?
It only flashes very briefly occasionally at power up. It doesn't aways flash and it's only the high order hours digit that I see flash. Actually, maybe the term "flash" is wrong. What I mean to say is that it comes on very briefly. It doesn't flash on-off-on...
I tried connecting pin 1 to pin 20 to force a reset. That still didn't start the clock. I'm beginning to wonder if the MCU isn't programmed with the clock code.
When does it flash, and for how long ?
I think RST=H is leds off, and leds on, means some code is running. Possibly serious supply droop crashes the MCU ?
It only flashes very briefly occasionally at power up. It doesn't aways flash and it's only the high order hours digit that I see flash. Actually, maybe the term "flash" is wrong. What I mean to say is that it comes on very briefly. It doesn't flash on-off-on...
Actually, I'm wrong. In fact all of the LEDs come on at one time or other although only one at a time. I also hear beeps from the speaker sometimes. This always happens only right on power up and never later.
It only flashes very briefly occasionally at power up. It doesn't aways flash and it's only the high order hours digit that I see flash. Actually, maybe the term "flash" is wrong. What I mean to say is that it comes on very briefly. It doesn't flash on-off-on...
Actually, I'm wrong. In fact all of the LEDs come on at one time or other although only one at a time. I also hear beeps from the speaker sometimes. This always happens only right on power up and never later.
Also try better (direct) Pin 20 - Pin 10 decoupling, the design seems to have a diode between the caps and actual power pins.... - seems to allow 3V or 5v power.
It only flashes very briefly occasionally at power up. It doesn't aways flash and it's only the high order hours digit that I see flash. Actually, maybe the term "flash" is wrong. What I mean to say is that it comes on very briefly. It doesn't flash on-off-on...
Actually, I'm wrong. In fact all of the LEDs come on at one time or other although only one at a time. I also hear beeps from the speaker sometimes. This always happens only right on power up and never later.
Also try better (direct) Pin 20 - Pin 10 decoupling, the design seems to have a diode between the caps and actual power pins.... - seems to allow 3V or 5v power.
I soldered a 0.1 uf cap between 10 and 20 and that didn't help.
C5 (100nF) appears to be the originaly intended decoupling cap for the Cpu, but, oh boy, its connections to 5V and Gnd are very far from any reasonable standpoint.
Please David, don't feel offended, but I use this technic with myself, when tired to search for any reasonable cause of failure. That said, the next question is: have you ever checked if there are any j or y or even v-alike pin bends at the cpu, so the bent pin was not completely inserted into the 20-pin socket?
I have done this before, more than I like to accept as an eventual failure, so I feel confortable to mention them, as a possible cause of misfunction. Being in a hurry, or tired are bad enemys; we must fight against them. Poor eyes and lighting conditions are the next ones.
C5 (100nF) appears to be the originaly intended decoupling cap for the Cpu, but, oh boy, its connections to 5V and Gnd are very far from any reasonable standpoint.
Please David, don't feel offended, but I use this technic with myself, when tired to search for any reasonable cause of failure. That said, the next question is: have you ever checked if there are any j or y or even v-alike pin bends at the cpu, so the bent pin was not completely inserted into the 20-pin socket?
I have done this before, more than I like to accept as an eventual failure, so I feel confortable to mention them, as a possible cause of misfunction. Being in a hurry, or tired are bad enemys; we must fight against them. Poor eyes and lighting conditions are the next ones.
Bent pins was one of the first things I checked. I just now removed the CPU again and verified that there are none. It's too bad since that would be easy to fix! :-)
Truth is that, sometimes, searching for evident causes of failure, can be a sure path to cause more defects than you already have.
There is a brazilian expression about dealing with messed things. Trying to translate as close as possible to the original meaning, without being offensive to anyone:
It's like recovering some discarded child diapers, trown at the trash can. The more you handles it, the worse it gets.
Excellent is the fact you're facing this chalenge with a bunch of positive forward thinking and good humor.
Its only now that I have noticed that the upper diode (1N4007) is forward mounted, in series, between 5V and cpu pin 20 (Vcc)? And the lower diode (also 1N4007) is forward mounted too, FROM the 3V connection pins, towards cpu pin 20.
Without any decoupling caps, at all!
Seems to be intended for a 3V battery to be conected to those pins.
Aux power for memory retention???
Time keeping, but without display scanning (where are any other provisions for it?), in order to avoid draining the battery, till exhaustion?
Every time, a surprise. Isn't it some delayed prank, from the passed april's first?
Truth is that, sometimes, searching for evident causes of failure, can be a sure path to cause more defects than you already have.
There is a brazilian expression about dealing with messed things. Trying to translate as close as possible to the original meaning, without being offensive to anyone:
It's like recovering some discarded child diapers, trown at the trash can. The more you handles it, the worse it gets.
Excellent is the fact you're facing this chalenge with a bunch of positive forward thinking and good humor.
I'm beginning to wonder if the MCU is defective. Maybe I'll order another $2 clock kit and try its MCU. It's cheaper than buying an MCU chip and programming it myself!
@David: Sorry to hear your clock is misbehaving. Your solder job looks fine. Just curious which Ebay seller you got it from and if you plan to reorder from the same seller.
@David: Sorry to hear your clock is misbehaving. Your solder job looks fine. Just curious which Ebay seller you got it from and if you plan to reorder from the same seller.
This is where I got it. I'm ordering another to see if I got a bad CPU chip.
Comments
Having only one son, does not make it fair, nor good, since you can't compare something against nothing.
Aniway. Lets try to determine if the cpu is outputing and the display is receiving any scan pulses at all.
You've need to use your scope to do this check.
If you don't have a schematic of your board, the one I've linked before could be used, as a guide.
Are you using the scope probe at 1x or 10x position?
Also, have you verifyed that RST (pin1) is steady near GND level? It would only go high (>3.5V) during the short time the 10uF cap is charging, aka, reseting the Cpu.
I must leave for a while. Be back at the end of the day. Hope to hear some good news, from you, when I return.
A clever paisano of yours, recognizing that the 2051 used a simple protocol (not like the SX!), made his own 2051 burner with an Arduino. I like that idea a lot. Except I'd use a Propeller.
The Keil evaluation assembler isn't all that big (a 77MB download) but has too many conditions that render it unsuitable for the 2051. Fortunately there are competent and free 8051 assemblers. Think that's the direction I'll take today - a free assembler and a diy P1-based chip burner. The 12V business is no problem at all.
Edit: On second thought, the AT89C2051 and its Nuvoton equivalent just aren't worth the effort. Twelve clocks per cycle and an old fuddy-duddy architecture...the nut didn't fall far from the tree on this one! You can spend the same $1.40 for a slightly less-old PIC that will run rings around them.
Some transistors have different pinouts. Could that be the cause?
Is there a link to the schematic?
That PCB looks to shunt the resistor-fed LEDs to ground, so both A & K lines pull down.
To pull down, the MCU needs to at least start running. At reset, all pins are lightly hi = LEDS off.
I think RST=H is leds off, and RST release -> leds on, means some code is running. Possibly serious supply droop crashes the MCU ?
Also try better (direct) Pin 20 - Pin 10 decoupling, the design seems to have a diode between the caps and actual power pins.... - seems to allow 3V or 5v power.
C5 (100nF) appears to be the originaly intended decoupling cap for the Cpu, but, oh boy, its connections to 5V and Gnd are very far from any reasonable standpoint.
Please David, don't feel offended, but I use this technic with myself, when tired to search for any reasonable cause of failure. That said, the next question is: have you ever checked if there are any j or y or even v-alike pin bends at the cpu, so the bent pin was not completely inserted into the 20-pin socket?
I have done this before, more than I like to accept as an eventual failure, so I feel confortable to mention them, as a possible cause of misfunction. Being in a hurry, or tired are bad enemys; we must fight against them. Poor eyes and lighting conditions are the next ones.
There is a brazilian expression about dealing with messed things. Trying to translate as close as possible to the original meaning, without being offensive to anyone:
It's like recovering some discarded child diapers, trown at the trash can. The more you handles it, the worse it gets.
Excellent is the fact you're facing this chalenge with a bunch of positive forward thinking and good humor.
Its only now that I have noticed that the upper diode (1N4007) is forward mounted, in series, between 5V and cpu pin 20 (Vcc)? And the lower diode (also 1N4007) is forward mounted too, FROM the 3V connection pins, towards cpu pin 20.
Without any decoupling caps, at all!
Seems to be intended for a 3V battery to be conected to those pins.
Aux power for memory retention???
Time keeping, but without display scanning (where are any other provisions for it?), in order to avoid draining the battery, till exhaustion?
Every time, a surprise. Isn't it some delayed prank, from the passed april's first?
Bourbon and poor choices next. Sign me up!
https://www.ebay.com/itm/272590606700
Is the pin-mapping the same ? - can one MCU be used to test another board ?
Have you ever tried to use your oscilloscope, to check if there are any refreshing/scanning activity at the display pins, coming from the cpu?
I cuould only remember you've did some checks at the crystal pins, with your probe set in x10 mode.