RIVA128ZX Datasheet, PDF (63/85 Pages) STMicroelectronics – 128-BIT 3D MULTIMEDIA ACCELERATOR

128-BIT 3D MULTIMEDIA ACCELERATOR
RIVA128ZX
12 IN-CIRCUIT BOARD TESTING
The RIVA128ZX has a number of features designed to support in-circuit board testing. These include:
• Dedicated test mode input and dual-function test mode select pins selecting the following modes:
- Pin float
- Parametric NAND tree
- All outputs driven high
- All outputs driven low
• Checksum test
• Test registers
12.1 TEST MODES
Primary test control is provided by the dedicated TESTMODE input pin. The RIVA128ZX is in normal op-
erating mode when this pin is deasserted. When TESTMODE is asserted, MP_AD[3:0] are reassigned as
TESTCTL[3:0] respectively. Test modes are selected asynchronously through a combination of the pin
states shown in Table 21.
Table 21. Test mode selection and descriptions
Test mode
TESTCTL[3:0]
Description
3210
Parametric 1 0 1 0 A single parametric NAND tree is provided to give a quiescent environ-
NAND tree
ment in which to test VIL and VIH without requiring core activity.
This capability is provided in the pads by chaining all I and I/O paths to-
gether via two input NAND gates. The chain begins with one input of the
first NAND gate tied to VDD while the other input is connected to the first
device pin on the NAND tree. The output of this gate then becomes the in-
put of the next NAND gate in the tree and so on until all pad input paths
have been connected. The final NAND gate output is connected to an out-
put-only pin whose normal functionality is disabled in NAND tree mode.
The NAND tree length is therefore equal to the number of I and I/O pins in
the RIVA128ZX. Output -only pins are not connected into the NAND tree.
Pin float
1 1 0 0 All pin output drivers are tristated in this test mode so that pin leakage
current (IIL,IIH,IOZL,IOZH) can be measured.
Outputs high 1 1 1 0 All pin output drivers drive a high output state in this test mode so that
output high voltage (VOH at IOH) can be measured.
Outputs low 1 1 1 1 All pin output drivers drive a low output state in this test mode so that out-
put low voltage (VOL at IOL) can be measured.
12.2 CHECKSUM TEST
The RIVA128ZX hardware checksum feature sup-
ports testing of the entire pixel datapath at full video
rates from the framebufferthrough to the DAC inputs.
Each of the three RGB colors can be tested to pro-
vide a correlation between the intended and actual
display. Checksums are accumulated during active
(unblanked) display. Note that the checksum mech-
anism does not check the DAC outputs (i.e. what is
physically being displayed on the monitor).
For a given image (which can be a real application’s
image or a specially prepared test card), theoretical-
ly derived checksum values can be calculated for a
selected RGB color, which are then compared with
the RIVA128ZX hardware checksum value. Alterna-
tively the checksum value from a known good chip
can be used as the reference.
Hardware checksum accumulation is not affected by
the horizontal and vertical synchronization wave-
forms or timings. Any discrepancy between the cal-
culated and RIVA128ZX hardware accumulated
checksum values therefore indicates a problem in
the device or system being tested. Details of pro-
gramming the RIVA128ZX checksum are given in
the RIVA128ZX Programming Reference Manual
[2].
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