Datasheet

19
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USBN9603/USBN9604
5.0 MICROWIRE/PLUS Interface
The MICROWIRE/PLUS interface allows the device to function as a CPU or microcontroller peripheral via a serial interface.
This mode is selected by pulling the MODE1 pin high and the MODE0 pin low. The MICROWIRE/PLUS mode uses the chip
select (
CS), serial clock (SK), serial data in (SI) and serial data out (SO) pins, as shown in Figure 14.
5.1 OPERATING COMMANDS
The MICROWIRE/PLUS interface is enabled by a falling edge of
CS and reset with a rising edge of CS. Data on SI is shifted
in after the rising edge of SK. Data is shifted out on SO after the falling edge of SK. Data is transferred from/to the Shift
register after the falling edge of the eighth SK clock. Data is transferred with the most significant bit first. Table 2 summarizes
the available commands (CMD) for the MICROWIRE/PLUS interface.
Note: A write operation to any register always reads the contents of the register after the write has occurred, and shifts out
that data in the next cycle. This read does not clear the bit in the respective registers, even for a Clear on Read (CoR) type
bit, with one exception: writing to the TXDx (transmit data) registers, which causes undefined data to be read during the next
cycle.
Table 2. Command/Address Byte Format
Byte Transferred
Sequence Initiated
1
1. 1 cycle = 8 SK clocks. Data is transferred after the 8th SK of 1 cycle.
CMD ADDR
Cycle Description
10543210
0 0 RADDR
(read)
1
2
Shift in CMD/RADDR; shift out previous read data
Shift in next CMD/ADDR; shift out RADDR data
0 1 x 1 no action; shift out previous read data (do not clear CoR bits)
1 0 WADDR
(normal write)
1
2
Shift in CMD/WADDR; shift out previous read data
Shift in WADDR write data; shift out WADDR read data (do
not clear CoR bits)
1 1 WADDR
(burst write)
1
2-n
Shift in CMD/WADDR; shift out previous read data
Shift in WADDR write data; shift out WADDR read data (do
not clear CoR bits); terminate this mode by pulling
CS high
SO
SK
SI
0x00
0x3F
DATA_IN
CS
Data Out
Data In
Register File
DATA_OUT
ADDR
Address
Figure 14. MICROWIRE/PLUS Interface Block Diagram
SHIFT
CMD1-0
SYNC
Obsolete