LM98503 datasheet(21/25 Pages) NSC

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Serial Interface Read/Write Description

1.0 Writing to the Serial Registers

To write to the serial registers, the timing diagram shown in

Figure 13 must be met. First CE is toggled low. SI DATA may

then be clocked in, and the data present on the rising edge of

the serial clock is loaded in. The data continues to be clocked in,

until CE toggles high. The data present in the register is the last

13 bits of data sent before CE toggled high. Therefore, for

example, if 20 bits were sent when CE was toggled low, the first

7 bits were discarded, and the data loaded are the remaining 13

bits. As seen in Figure 13, these 13 bits are composed of 8 data

bits, 4 address bits, and 1 read/write bit. When writing to the

registers, the read/write bit must be low. When CE toggles high,

the register is written to, and the LM98503 now functions with

this new data.

2.0 Reading the Serial Registers

To read the serial registers, the timing diagram shown in Figure

12 must be met. When CE is toggled low, and data is loaded as

described above in the writing sequence. When CE toggles

high, the new 13 bit word is considered, except this time the

read/write bit should be a 1 indicating a read. The 8 data bits are

not considered, but act only as place holders. When CE toggles

low again, the data that resides at the address considered in the

previous read or write routine, begins clocking out SO DATA.

The data streams out MSB-LSB as shown in Figure 12. Whether

a read or a write was invoked in the previous sequence, the SO

DATA will clock out the contents of the address considered in

the previous sequence.

LM98503 데이터시트(PDF) 21 Page - National Semiconductor (TI)