SPRUJB3 March 2024 AM67 , AM67A , TDA4AEN-Q1 , TDA4VEN-Q1
OLDITX supports data loopback mode to check for DC faults in the digital (parallel to serial conversion logic) and analog (LVDS transmitter) data signal path.
In the loopback test mode, the sending module (DSS DISPC) drives all OLDITX input signals (data and sync) to either all 1s or 0s. All 1s and all 0s will be captured as a static 1 or 0 at the output of the LVDS loopback receiver (enabled only during the test mode). To ensure that there are no faults in the parallel to serial conversion logic path, a simple pattern check of 1s or 0s is be performed on the serializer data and reported back along with the LVDS loopback value. These signals are then passed back to DSS and mapped to the DSS0_VP_DSS_OLDI_LB[9-0] LBRDATA register field for test software to read.
For loopback testing of the clock differential output signals, OLDITX drives all 0s or 1s pattern (based on the DSS0_VP_DSS_OLDI_CFG[10] LBDATA register bit configuration) instead of the normal clock pattern, when the loopback test is enabled.
Since there is no de-serializer in the loopback path, the loopback mode is intended for facilitating a system diagnostic testing with a constant data output (all 0s or 1s) at low-speed. In normal operation, the loopback mode must be disabled.
When looback is enabled in DSS0_VP_DSS_OLDI_CFG[9] LBEN register bit, the loopback of data in this order from MSB to LSB {all_0_1[4:0], oldi_ch_ret_clock, oldi_ch_ret_data[3:0]} will be returned in DSS0_VP_DSS_OLDI_LB[9-0] LBRDATA register field.
Verifying loopback
Set up OLDITX for a single mode and select the DSS input data. Configure the parameters as shown for either Case 1 or Case 2 below. Set DSS0_VP_DSS_OLDI_CFG[9] LBEN = 1 and enable OLDITX to start sending data. Check after 10 pixel clock periods.
Case 1, all 0’s stuck-at test:
Check:
Case 2, all 1’s stuck-at test:
Check:
Note that DSS0_VP_DSS_OLDI_LB[3] LBRDATA = 1. In functional operation, the LVDS A30:A36 in 18-bit single mode are not being driven by input data, rather all 0’s. In loopback mode, each of A30:A36 is driven by OLDI_0_DE. In other single modes, the "reserved or NA" bit fields, as described in the LVDS data format mapping tables in Section 12.9.1.2.2, DSS LVDS Interface, are driven by OLDI_0_DE in loopback mode.