DS2148 datasheet(24/75 Pages) DALLAS

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DS2148/Q48

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5.2

Parallel Port Operation

When using the parallel interface on the DS2148 (BIS1 = 0) the user has the option for either multiplexed

bus operation (BIS1 = 0, BIS0 = 0) or nonmultiplexed bus operation (BIS1 = 0, BIS0 = 1). The DS2148

can operate with either Intel or Motorola bus timing configurations. If the PBTS pin is tied low, Intel

timing will be selected; if tied high, Motorola timing will be selected. All Motorola bus signals are listed

in parenthesis (). See the timing diagrams in Section 12 for more details.

5.3

Serial Port Operation

Setting BIS1 = 1 and BIS0 = 0 enables the serial bus interface on the DS2148. Port read/write timing is

unrelated to the system transmit and receive timing, allowing asynchronous reads or writes by the host.

See Section 12 for the AC timing of the serial port. All serial port accesses are LSB first. See Figure 5-1,

Figure 5-2, Figure 5-3, and Figure 5-4 for more details.

Reading or writing to the internal registers requires writing one address/command byte prior to

transferring register data. The first bit written (LSB) of the address/command byte specifies whether the

access is a read (1) or a write (0). The next 5 bits identify the register address. Bit 7 is reserved and must

be set to 0 for proper operation.

The last bit (MSB) of the address/command byte is the burst mode bit. When the burst bit is enabled

(B = 1) and a READ operation is performed, addresses 0 through 15h are read sequentially, starting at

address 0h. And when the burst bit is enabled and a WRITE operation is performed, addresses 0 through

16h are written sequentially, starting at address 0h. Burst operation is stopped once address 15h is read.

See Figure 5-5 and Figure 5-6 for more details.

All data transfers are initiated by driving the CS* input low. When input clock-edge select (ICES) is low,

input data is latched on the rising edge of SCLK and when ICES is high, input data is latched on the

falling edge of SCLK. When output clock-edge select (OCES) is low, data is output on the falling edge of

SCLK and when OCES is high, data is output on the rising edge of SCLK. Data is held until the next

falling or rising edge. All data transfers are terminated if the CS* input transitions high. Port control logic

is disabled and SDO is 3-stated when CS* is high.

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