3 ms·

What was the purpose of something like this? Like, why would a designer have chosen this over a microprocessor like the Intel 4004 from 5 years prior?

vlovich123 6y ago
It’s implied in the article I think. > In 1977, the MC14500B cost $7.58 in quantities of 100 ($32 in current dollars), which seems expensive. However, at the time, an 8080A CPU cost $20 and a Z80 cost $50 ($85 and $215 in current dollars) so there was a significant cost saving to the MC14500B.5 However, the steady fall of processor prices soon made the MC14500B less attractive. Perhaps in 1977 you couldn’t source the 4004 in the quantities you might need to make a product leaving you only with more expensive contemporary processors?
- kens 6y ago
  Yes, cost was an issue. Also complexity; the documentation says: "Computers and microcomputers may also be used [for control tasks], but they tend to overcomplicate the task and often require highly trained personnel to develop and maintain the system. A simpler device, designed to operate on inputs and outputs one-at-a-time and configured to resemble a relay system, was introduced. These devices became known to the controls industry as Programmable Logic Controllers (PLC). The Motorola MCI4500B Industrial Control Unit (ICU) is the monolithic embodiment of the PLC's central architecture." I couldn't find data on how popular the MC14500B was, but I think microcontrollers such as the Texas Instruments TMS1000 were much more popular.
  - retrac 6y ago
    Yes, in hindsight with our computer-centric perspective today, it seems like programming the MC14500 is something you'd get CS and programming people to do. But the user manual has sections on how to translate ladder logic and similar control logic into a program counter circuit and appropriate code, step by step. If someone was familiar with industrial control and basic digital electronics, I think the manual is about all they would need. The same can't be said for most other microcontrollers which are indisputably full computers, with all of their complexity.
adrian_b 6y ago
See my post from above. In industrial control there are a lot of processes with a large number of on/off sensors and actuators. One-bit programmable controllers like 14500B were good enough to handle those. In such old installations, the sensors and actuators that could not be handled by one-bit controllers were handled by analog controllers, unlike in modern installations, where a MCU handles digitally not only the Boolean variables but also the analog values through ADCs and DACs, so arithmetic computations are also required, besides the logic operations that could already be performed by something like 14500B.
dboreham 6y ago
I was early in my career at the time, and remember looking at the datasheet and asking myself the same question. Reflecting back, I think the sibling post that mentions an upgrade of an older discrete TTL PLC system could be the bulk of the target market. So while it was unlikely someone would begin a clean new design with a 1-bit CPU, there were older systems that already had the 1-bit architecture that suited this device for a mid-life re-do. Besides that, semi vendors have on occasion been known to manufacture a device that has no market success to due to poor product/market fit, or technology bypassing it by the time it was finished. Most devices were originally made as custom designs for some specific customer or application so perhaps there's a boatload of these in some 1970's car.

vlovich123 6y ago

It’s implied in the article I think. > In 1977, the MC14500B cost $7.58 in quantities of 100 ($32 in current dollars), which seems expensive. However, at the time, an 8080A CPU cost $20 and a Z80 cost $50 ($85 and $215 in current dollars) so there was a significant cost saving to the MC14500B.5 However, the steady fall of processor prices soon made the MC14500B less attractive. Perhaps in 1977 you couldn’t source the 4004 in the quantities you might need to make a product leaving you only with more expensive contemporary processors?

kens 6y ago
Yes, cost was an issue. Also complexity; the documentation says: "Computers and microcomputers may also be used [for control tasks], but they tend to overcomplicate the task and often require highly trained personnel to develop and maintain the system. A simpler device, designed to operate on inputs and outputs one-at-a-time and configured to resemble a relay system, was introduced. These devices became known to the controls industry as Programmable Logic Controllers (PLC). The Motorola MCI4500B Industrial Control Unit (ICU) is the monolithic embodiment of the PLC's central architecture." I couldn't find data on how popular the MC14500B was, but I think microcontrollers such as the Texas Instruments TMS1000 were much more popular.
- retrac 6y ago
  Yes, in hindsight with our computer-centric perspective today, it seems like programming the MC14500 is something you'd get CS and programming people to do. But the user manual has sections on how to translate ladder logic and similar control logic into a program counter circuit and appropriate code, step by step. If someone was familiar with industrial control and basic digital electronics, I think the manual is about all they would need. The same can't be said for most other microcontrollers which are indisputably full computers, with all of their complexity.

adrian_b 6y ago

See my post from above. In industrial control there are a lot of processes with a large number of on/off sensors and actuators. One-bit programmable controllers like 14500B were good enough to handle those. In such old installations, the sensors and actuators that could not be handled by one-bit controllers were handled by analog controllers, unlike in modern installations, where a MCU handles digitally not only the Boolean variables but also the analog values through ADCs and DACs, so arithmetic computations are also required, besides the logic operations that could already be performed by something like 14500B.

dboreham 6y ago

I was early in my career at the time, and remember looking at the datasheet and asking myself the same question. Reflecting back, I think the sibling post that mentions an upgrade of an older discrete TTL PLC system could be the bulk of the target market. So while it was unlikely someone would begin a clean new design with a 1-bit CPU, there were older systems that already had the 1-bit architecture that suited this device for a mid-life re-do. Besides that, semi vendors have on occasion been known to manufacture a device that has no market success to due to poor product/market fit, or technology bypassing it by the time it was finished. Most devices were originally made as custom designs for some specific customer or application so perhaps there's a boatload of these in some 1970's car.