Hot answers tagged

64

Because it used to be necessary. While a battery-powered real-time clock is standard today, this wasn’t always the case. The very first IBM 5150 did not include an RTC chip; the system clock was maintained by the PIT interrupt running on the CPU, which in particular meant that disabling interrupts halted the system clock. When the computer was turned off, ...


43

From a CNN article I found about one such card: Most pre-1997 PCs had real-time clock chips ticking off six-digit dates (mm-dd-yy) translated by the BIOS into eight-digit dates indicating the proper century. Most BIOSes aren't programmed to calculate the proper century after January 1, 2000, potentially causing system failure. The Evergreen [Year 2000 ...


27

Or was the clock maintained in software, and based off of something like the 18.2 Hz system timer interrupt? This is exactly how time was tracked; you can see the implementation of the timer tick handler in the IBM PC Technical Reference, page A-77. It updates a counter, stored in memory as a double word at 0x0040:0x006C, and checks for elapsing days, ...


13

Or was the clock maintained in software, and based off of something like the 18.2 Hz system timer interrupt? Exactly that. It is a 32 bit counter incremented by one every time INT 8 is triggered by the 8253 counter #3 (via INT 0). If the latter, was it common to lose clock accuracy if the timer rate was changed by a running program? That depends much on ...


11

It was necessary, because the early hardware did not contain a Real Time Clock (RTC) chip. The first IBM PC model to have an RTC chip as a standard feature and supported by BIOS was the IBM PC/AT, and earlier models could be retrofitted with an add-on RTC ISA card. So the models before AT cannot possibly know the current time automatically after powering the ...


9

Most likely, the two RTC devices would conflict, since they will probably rely on the same chip select line and base address $D80000. Technically, the A1200 clock port and the A1200 expansion "trap-door" slot can support 2 separate clock port devices, since there are two chip selects. These are called the "RTC" CS, which uses $D80000-$D8FFFF, and the "SPARE"...


7

TL; DR: Because it is not a 16-bit device, as it has a multiplexed 8-bit address/data bus, and giving 64 IO addresses from the 256 reserved to PC motherboard devices would have been too much, so access to it was split into two IO ports, one to send address and another to read/write data. As the chip does not have a separate address and data buses, they are ...


5

Edit: Made a mistake, JustMe has the correct answer. I was thinking the XT had an RTC, but it was an AT specific thing so the rationale for the 8 bit writes is chipset related and not directly on the 8086 bus. Old post below. TL;DR: Because the CMOS chip might only have an 8 bit data interface. Full Detail: An 8 bit I/O operation and a 16 bit I/O operation ...


4

These NiMH batteries usually have very simple charging circuitry and replacing them with generic 3 or 6 x 1.2V NiMH cells in series will almost certainly be fine. I remember there were even (3.6V) battery packs being sold in the past for just this purpose. As the resulting capacity will be higher than that of the original batteries, they will need more time ...


4

Expanding on the comment made by @pipe: Most if not all batteries originally used on the various Amigas and contemporary peripherals are rechargable NiCd (Nickel Cadmium) cells which are prone to leak. If the battery is a common type, there is likely a drop-in replacement NiMH (Nickel Metal Hydride) battery which is rechargable and far less likely to leak, ...


4

If the latter, was it common to lose clock accuracy if the timer rate was changed by a running program? It was certainly possible, yes; it's hard to say how common this kind of distortion was, but it was fairly easily avoidable. A well-behaved program that hooks the timer interrupt needs to call the original handler at its original rate. If it changes the ...


2

For PC XT types, there were multifunction cards using a MC58167 from National Semiconductors. Other RTC chips were also used.


2

It fits. Okay, so I'd swear that I tried this when I got the card and it didn't fit. But it took someone asking for a photo for me to try it again in a 5150 and.... Now it is a little bit awkward in a 5160 because it slightly blocks the adjacent card but it DOES in fact fit. (facepalm)


1

To answer this with absolute certainty, you'd have to examine each cartridge on its own, particularly those that weren't made by Nintendo. I'm not sure anyone has ever done that, but people have looked at quite a number of cartriges (e.g., here and here), and Nintendo cartridges for the GB/GBC all appear to use the Mitsumi MM1134 system supervisor IC (or ...


1

Standard PC hardware includes a real-time clock powered by a battery I guess this is a valid assumption since IBM PC AT. Older PCs (PC, PCjr, XT) has no RTC by default (due to Wikipedia).


1

I had a leaky battery on my Apollo 1240 card (it is the same PCB as the 1260) and desoldered it and replaced it with a Panasonic VL1220-1HFE rechargeable coin battery. Now the original battery had three pins, and the panasonic has two but I think the positive and negative terminals are marked on the card so just make sure you solder onto the right holes. The ...


Only top voted, non community-wiki answers of a minimum length are eligible