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Boundary scan results to IC mapping



Boundary scan results to IC mapping

 

# bits Bit position IC(s)
0-87 199s
88-175 191s
176-263 185s
264-482
483-701
702-789
799-1051
1052-1139
1140-1227
1228-1315
1316-1534
1535-1753
1754-1841
1842-2103
2104-2564 77, 76, 90

 

This table was reverse engineered from recording the jtag bus while the boundary scan occured (well at least the start of it). I had already worked out the order the ICs were placed in the JTAG chain and the fact the video memory has 88 boundary scan registers (from the datasheet). From there it was a case of recognising the repeated 88 bit patterns from the scan to establish the number of bits in the Sega BGA ICs.

Boundary Scan Bit Position

The following table can be used to identify the pin on the video ICs that the boundary scan is theoretically referring to. Don’t assume that if you have one of these bit positions come up that there is a fault with that IC, however its a good place to work out which pins to look at.

 

 

Pin Desc Pin # IC199s IC191s IC185s IC162 IC99 IC91 IC85 IC62
VID_Q7
VID_Q6
VID_Q5
VID_Q4
VID_Q3
VID_Q2
VID_Q1
VID_Q0
HIT
VID_OE
VID_CKE
VID_QSF
VID_Q15
VID_Q14
VID_Q13
VID_Q12
VID_Q11
VID_Q10
VID_Q9
VID_Q8
RESET
DRAM_BS1
DRAM_BS0
DRAM_A8
DRAM_A7
DRAM_A6
DRAM_OP2
DRAM_OP1
PALU_A5
PALU_A4
PALU_A3
PALU_EN1
PALU_WE
PALU_OP2
PALU_BE3
PALU_BE2
PALU_DX3
PAUL_DX2
PALU_DQ31
PALU_DQ30
PALU_DQ29
PALU_DQ28
PALU_DQ27
PALU_DQ26
PALU_DQ25
PALU_DQ24
PALU_DQ23
PALU_DQ22
PALU_DQ21
PALU_DQ20
PALU_DQ19
PALU_DQ18
PALU_DQ17
PALU_DQ16
PALU_DQ15
PALU_DQ14
PALU_DQ13
PALU_DQ12
PALU_DQ11
PALU_DQ10
PALU_DQ9
PALU_DQ8
PALU_DQ7
PALU_DQ6
PALU_DQ5
PALU_DQ4
PALU_DQ3
PALU_DQ2
PALU_DQ1
PALU_DQ0
PALU_DX1
PALU_DX0
PALU_BE1
PALU_BE0
PALU_OP1
PALU_OP0
PALU_EN0
PALU_A2
PALU_A1
PAUL_A0
DRAM_OP0
DRAM_EN
DRAM_A5
DRAM_A4
DRAM_A3
DRAM_A2
DRAM_A1
DRAM_A0

 

 

Memory Test Faults

The video board memory test gives a range of faults. It does seem however that it normally fails an entire group of ram ICs when only one of them is actually faulty. Another interesting fact is the IC numbers the memory test will give you often don’t exist on the video board. That’s because it seems to be reporting IC numbers from the step 1. 5 board. On the step 1. 5 board you can see the ICs that are reported to have failed next to empty pads marked with the IC number that needs to be replaced.

 



  

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