High-Speed Digital Interfacing with QSPI

The MAX148/MAX149 can interface with QSPI using

CPHA = 0). This QSPI circuit can be programmed to do a

conversion on each of the eight channels. The result is

stored in memory without taxing the CPU, since QSPI

incorporates its own microsequencer.

The MAX148/MAX149 are QSPI compatible up to the

maximum external clock frequency of 2MHz.

TMS320LC3x Interface

Figure 21 shows an application circuit to interface the

MAX148/MAX149 to the TMS320 in external clock mode.

The timing diagram for this interface circuit is shown in

Figure 22.

Use the following steps to initiate a conversion in the

MAX148/MAX149 and to read the results:

1) The TMS320 should be configured with CLKX

(transmit clock) as an active-high output clock and

CLKR (TMS320 receive clock) as an active-high

input clock. CLKX and CLKR on the TMS320 are

tied together with the MAX148/MAX149’s SCLK

input.

2) The MAX148/MAX149’s CS pin is driven low by the

TMS320’s XF_ I/O port to enable data to be clocked

into the MAX148/MAX149’s DIN.

3) An 8-bit word (1XXXXX11) should be written to the

MAX148/MAX149 to initiate a conversion and place

the device into external clock mode. Refer to Table

1 to select the proper XXXXX bit values for your

specific application.

4) The MAX148/MAX149’s SSTRB output is monitored

via the TMS320’s FSR input. A falling edge on the

SSTRB output indicates that the conversion is in

progress and data is ready to be received from the

MAX148/MAX149.

5) The TMS320 reads in one data bit on each of the

next 16 rising edges of SCLK. These data bits rep-

resent the 10 + 2-bit conversion result followed by

4 trailing bits, which should be ignored.

6) Pull CS high to disable the MAX148/MAX149 until

the next conversion is initiated.

+2.7V to +5.25V, Low-Power, 8-Channel,

Serial 10-Bit ADCs

______________________________________________________________________________________

21

CS

SCLK

DIN

SSTRB

DOUT

START

SEL2

SEL1

SEL0

UNI/BIP SGL/DIF

PD1

PD0

MSB

B8

S1

S0

HIGH

IMPEDANCE

HIGH

IMPEDANCE

Figure 22. TMS320 Serial-Interface Timing Diagram