FW: 8250 family differences

[glenn.f...@gmail.com]

Sharing a message from Terry who is traveling and currently unable to post to the SEBHC list…

 

 

 

Look at all the "pin compatible" flavors here and the subtle differences between them.

 

Norberto encountered similar differences in the 8251 behavior on the cassette board.

 

I tend to think of logic chips as interchangeable but it's clear that LSI is not necessarily interchangeable.

 

Tas

 

 

[Lee Hart]

Very true. Many 2nd sources weren't licensed, so their copies don't always behave exactly the same.

I use the original 8250 in my Z80-SIO card. The original version was slow (thus the Heath 74LS74 pulse stretcher circuit). The later 8250B version fixed this. The 8250A actually came out later. Its main virtue is that it is faster, and works with a 4 MHz Z80.

The 82C50 and 16C450 are CMOS versions. They work the same with Heath software, but there are some subtle differences if you start programming them right down to the "bare metal".

The 16C550 is quite a bit different. It *may* work in the same socket with old software, but several of the pins have been re-assigned, and it has internal FIFOs that need program changes to be used.

Lee Hart

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