SPI/Microwire-Compatible
UART in QSOP-16
MAX3100
ONE BAUD PERIOD
RX
A
BAUD
BLOCK
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
MAJORITY
CENTER
SAMPLER
Figure 3. Start-Bit Timing
DATA
UPDATED
CS
SCLK
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
DIN
1
1
FEN
SHDN
TM
RM
PM
RAM
IR
ST
PE
L
B3
B2
B1
B0
DOUT
R
T
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Figure 4. SPI Interface (Write Configuration)
The receiver section receives data in serial form. The
MAX3100 detects a start bit on a high-to-low RX transi-
tion (Figure 3). An internal clock samples data at 16
times the data rate. The start bit can occur as much as
one clock cycle before it is detected, as indicated by
the shaded portion. The state of the start bit is defined
as the majority of the 7th, 8th, and 9th sample of the
internal 16x baud clock. Subsequent bits are also
majority sampled. Receive data is stored in an 8-word
FIFO. The FIFO is cleared if it overflows.
The on-board oscillator can use a 1.8432MHz or
3.6864MHz crystal, or it can be driven at X1 with a 45%
to 55% duty-cycle square wave.
SPI Interface
The bit streams for DIN and DOUT consist of 16 bits,
with bits assigned as shown in the
MAX3100
Operations
section. DOUT transitions on SCLK’s falling
edge, and DIN is latched on SCLK’s rising edge (Figure
4). Most operations, such as the clearing of internal
registers, are executed only on
CS’s
rising edge. The
DIN stream is monitored for its first two bits to tell the
UART the type of data transfer being executed (Write
Config, Read Config, Write Data, Read Data).
Only 16-bit words are expected. If
CS
goes high in the
middle of a transmission (any time before the 16th bit),
the sequence is aborted (i.e., data does not get written
to individual registers). Every time
CS
goes low, a new
16-bit stream is expected. An example of a write con-
figuration is shown in Figure 4.
7
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