UM0434 datasheet(369/390 Pages) STMICROELECTRONICS

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Nexus3 module

UM0434

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nex_rdy_b) and sets RWCS[DV]. This indicates that the device is ready for the next

access.

The data can then be read from RWD with the access method outlined in

Chapter 12.5:

Nexus3 register access through JTAG/OnCE on page 348,” using the Nexus register

index of 0xA; see

Table 216.

Note:

Only the nex_rdy_b signal and the DV and ERR bits within RWCS provide read/write access

status to the external development tool.

12.10.5

Block read access (Non-Burst Mode)

For a non-burst block read access, follow steps 1 and 2 outlined in

Chapter 12.10.4:

Single read access on page 369,” to initialize the registers, but using a value greater

than one (0x0001) for RWCS[CNT].

The Nexus block then arbitrates for the AHB system bus, and the read data is

transferred from the AHB to the RWD register. When the transfer has completed

without error (ERR = 0), the address from RWA is incremented to the next word size

(specified in the SZ field), and the number from the CNT field is decremented. Nexus

then asserts the

nex_rdy_b pin. This indicates that the device is ready for the next

access.

The data can then be read from RWD with the access method outlined in

Chapter 12.5:

Nexus3 register access through JTAG/OnCE on page 348,” using the Nexus register

index of 0xA, see

Table 216.

Repeat steps 3 and 4 in

Chapter 12.10.4: Single read access on page 369,” until the

CNT value is zero. When this occurs, RWCS[DV] is set to indicate the end of the block

read access.

12.10.6

Block read access (Burst Mode)

For a burst block read access, follow steps 1 and 2 outlined in

Chapter 12.10.4: Single

read access on page 369,” to initialize the registers, using a value of four (double-

words) for the CNT field and an SZ field indicating 64-bit access in RWCS.

The Nexus block then arbitrates for the AHB system bus and the burst read data is

transferred from the AHB to the data buffer (RWD register). For each access within the

burst, the address from the RWA register is incremented to the next double-word,

specified in the SZ field, and the number from the CNT field is decremented.

When the entire burst transfer has completed without error (ERR=0), Nexus then

asserts the

nex_rdy_b pin, and RWCS[DV] is set to indicate the end of the block read

access.

The data can then be read from the burst data buffer (RWD register) with the access

method outlined in

Chapter 12.5: Nexus3 register access through JTAG/OnCE on

page 348,” using the Nexus register index of 0xA; see Table 216.

Repeat step 3 until all double-word values are read from the buffer.

Note:

The data values must be shifted out 32-bits at a time, least significant bit first, that is double-

word read = two word reads from RWD.

Note:

The actual RWA and CNT values within RWCS are not changed when executing a block

read access, burst or non-burst. The original values can be read by the external

development tool at any time.

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