Rainbow Electronics MAX5259 - Manual (Page 10)

MAX5258/MAX5259
+3V/+5V, Low-Power, 8-Bit Octal DAC
with Rail-to-Rail Output Buffers
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Detailed Description
Serial Interface
At power-on, the serial interface and all DACs are
cleared and set to code zero. The serial data output
(DOUT) is set to transition on SCLK’s falling edge.
The MAX5258/MAX5259 communicate with micro-
processors (µPs) through a synchronous, 3-wire inter-
face (Figure 1). Data is sent MSB first and can be
transmitted in two 4-bit and one 8-bit (byte) packets, or
one 16-bit word. The first two bits are ignored. A 4-wire
interface adds a line for LDAC, allowing asynchronous
updating. Data is transmitted and received simultane-
ously.
Figure 2 shows the detailed serial-interface timing. Note
that the clock should be low if it is stopped between
updates. DOUT does not go into a high-impedance state
if the clock idles or CS is high.
Serial data is clocked into the data registers in MSB-first
format, with the address and configuration information
preceding the actual DAC data. Data is clocked in on
SCLK’s rising edge while CS is low. Data at DOUT is
clocked out 16 clock cycles later, either at SCLK’s falling
edge (default or mode 0) or rising edge (mode 1).
CS must be low to enable the device. If CS is high, the
interface is disabled and DOUT remains unchanged.
CS must go low at least 40ns before the first rising edge
of the clock pulse to properly clock in the first bit. With
CS low, data is clocked into the MAX5258/MAX5259’s
internal shift register on the rising edge of the external
serial clock. Always clock in the full 16 bits.
Serial Input Data Format and Control Codes
The 16-bit serial input format, shown in Figure 3, com-
prises two “don’t care” bits, three DAC address bits (A2,
A1, A0), three control bits (C2, C1, C0), and eight data
bits (D7…D0). The 6-bit address/control code configures
the DAC as shown in Table 1.
Pin Description
PIN NAME FUNCTION
1 OUTB DAC B Voltage Output
2 OUTA DAC A Voltage Output
3 GND Ground
4 V DD Power Supply
5 REF Reference Voltage Input
6 LDAC
Load DAC Input. Driving this asynchronous input low transfers the contents of each input register
to its respective DAC registers.
7 OUTE DAC E Voltage Output
8 OUTF DAC F Voltage Output
9 OUTG DAC G Voltage Output
10 OUTH DAC H Voltage Output
11 CS
Chip Select Input. Data is shifted in and out when CS is low. Programming commands are executed
when CS returns high.
12 SCLK
Serial Clock Input. Data is clocked in on the rising edge and clocked out on the falling edge
(default) or rising edge (A2 = 1; see Table 1).
13 DIN Serial Data Input. Data is clocked in on the rising edge of SCLK.
14 DOUT
Serial Data Output. Sinks and sources current. Data at DOUT can be clocked out on the falling
edge (mode 0) or rising edge (mode 1) of SCLK (Table 1).
15 OUTD DAC D Voltage Output
16 OUTC DAC C Voltage Output