1.2.5. Order of output of TDI and TMS bits passed over tapop.h

The Multi-ICE hardware contains 40-bit data registers so that scan chains with up to 40 bits are accessed efficiently. TDI, TDO, and TMS data is passed over tapop.h using a 40-bit type called ScanData40 constructed from a 32-bit word containing the least significant bits and a byte containing the most significant bits. This type is defined in tapop.h.

typedef struct ScanData40 {    unsigned32 low32;
    unsigned8 high8;
} ScanData40;

The bits are output as follows:

  1. Bit 0 of low32 to bit 31 of low32.

  2. Bit 0 of high8 to bit 7 of high8.

Similarly, for an output (TDO) block the first TDO bit input is placed in bit 0 of low32, and the last in bit 7 of high8.

If a data field is specified as reversed then the same data is written to, or read from, the Multi-ICE reversed data register. Bits are entered from the least significant bit of low32. For example, to write four bits of reversed data, fill bits 0 to 3 in low32. The bits enter the scan chain in the order bit 3, bit 2, bit 1, bit 0.

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