debs3759 wrote on 2023-06-14, 18:29:
Don't most 486 have JTAG? I thought even some 386 had it
Not the first 486DX's (CHMOS IV = 1 µm ?)
Not the first PGA 486SX's (CHMOS IV = 1 µm ?)
Not the first 487SX's (CHMOS IV = 1 µm ?)
Not the first low power 486DX's (CHMOS IV = 1 µm)
Not the first low power 486SX's (CHMOS IV = 1 µm)
But the first PQFP 486SX's had TDI, TDO, TMS, TCK. (CHMOS V = 0,8 µm ?)
Same with the first 486 DX 50. (CHMOS V = 0,8 µm ?)
The power supply current [mA] comparison of the first SX's is:
MHz / CHMOS IV / CHMOS V Percent / 487SX
16 / 525 / 450 (85,7 %) / 625
20 / 600 / 500 (83,3 %) / 775
25 / 700 / 560 (80 %) / 950
It seems like the first PGA 486SX's were produced in CHMOS IV (1 µm).
It seems like the first PQFP 486SX's were produced in CHMOS V (0,8 µm).
It seems like the first 487SX's were produced in CHMOS IV (1 µm).
With a 487SX present the PQFP 486SX introduces a Power Down Mode
MHz CHMOS IV CHMOS V
16 / 400 / 50
20 / 500 / 50
25 / 600 / 50
So, in fact, at 25 MHz 486SX / 487SX combo can draw 1550 mA, compared to a 486 DX with 700 mA.
The power supply current table of the first 486 DX's is interesting.
MHz Icc
25 700
33 900
50 1000
The input capacitance of the 25/33 MHz ones is 20 pF, whereas the 50 MHz variant has 13-17 pF.
Conclusion: It seems like the first 486DX's were produced in CHMOS IV (1 µm), but the first 50 MHz ones in CHMOS V (0,8 µm).
For the first 487SX's the input capacitance is also 20 pF.
The imput capacitance of the first PGA 486SX's is also 20 pF, whereas the first PQFP 486SX's have 6-10 pF.
Conclusion: It seems like the first PGA 486SX's were produced in CHMOS IV (1 µm) and have a disabled FPU, but the first PQFP 486SX's are in CHMOS V (0,8 µm) and have no FPU at all.
All values are taken from the book "Intel, Microprocessors, Volume I, 1992"