MAX1277/MAX1279
1.5Msps, Single-Supply, Low-Power, True-
Differential, 12-Bit ADCs with Internal Reference
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read the data without CPU intervention. Connect the V
L
pin to the TMS320C54_ supply voltage when the
MAX1277/MAX1279 are operating with an analog sup-
ply voltage higher than the DSP supply voltage. The
word length can be set to 8 bits with FO = 1 to imple-
ment the power-down modes. The CNVST pin must idle
high to remain in either power-down state.
Another method of connecting the MAX1277/MAX1279
to the TMS320C54_ is to generate the clock signals
external to either device. This connection is shown in
Figure 16, where serial clock (CLOCK) drives the
CLKR, and SCLK and the convert signal (CONVERT)
drive the FSR and CNVST.
The serial port must be set up to accept an external
receive-clock and external receive-frame sync.
The SPC register should be written as follows:
TXM = 0, external frame sync
MCM = 0, CLKX is taken from the CLKX pin
FSM = 1, burst mode
FO = 0, data transmitted/received as 16-bit words
This setup allows continuous conversion, provided that
the DRR is serviced before the next conversion.
Alternatively, autobuffering can be enabled when using
the buffered serial port to read the data without CPU
intervention. Connect the V
L
pin to the TMS320C54_
supply voltage when the MAX1277/MAX1279 are oper-
ating with an analog supply voltage higher than the
DSP supply voltage.
The MAX1277/MAX1279 can also be connected to the
TMS320C54_ by using the data transmit (DX) pin to
drive CNVST and the CLKX generated internally to
drive SCLK. A pullup resistor is required on the CNVST
signal to keep it high when DX goes high impedance
and 0001hex should be written to the DXR continuously
for continuous conversions. The power-down modes
may be entered by writing 00FFhex to the DXR (see
Figures 17 and 18).
DSP Interface to the ADSP21_ _ _
The MAX1277/MAX1279 can be directly connected to
the ADSP21_ _ _ family of DSPs from Analog Devices,
Inc. Figure 19 shows the direct connection of the
MAX1277/MAX1279 to the ADSP21_ _ _. There are two
modes of operation that can be programmed to interface
with the MAX1277/MAX1279. For continuous conver-
sions, idle CNVST low and pulse it high for one clock
cycle during the LSB of the previous transmitted word.
The ADSP21_ _ _ STCTL and SRCTL registers should be
Figure 15. Interfacing to the TMS320C54_ Internal Clocks
Figure 16. Interfacing to the TMS320C54_ External Clocks
