Rainbow Electronics MAX6963 User Manual

Page 12

MAX6960–MAX6963

4-Wire Serially Interfaced
8 x 8 Matrix Graphic LED Drivers

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24-Bit Transmissions

Twenty-four-bit transmissions are read/write, address-
and-data accesses to the MAX6960’s display memory
(Figure 8). This is direct access to display memory
because the memory address is included in the 24-bit
transmission, compared with an 8-bit transmission,
which uses the memory address stored in the global
display indirect address register. Twenty-four-bit trans-
missions provide the random-access method of updat-
ing a plane of display memory of the MAX6960. It is the
most suitable display update method if the host system
builds an image directly in a display memory plane,
rather than in host local memory.

Host 4-Wire Serial Interface

Serial Addressing

The MAX6960 communicates to the host through a 4-
wire serial interface. The interface has three inputs:
clock (CLK), chip select (

CS), and data in (DIN), and

one output, data out (DOUT).

CS must be low to clock

data into the device, and DIN must be stable when
sampled on the rising edge of CLK. DOUT is used for
read access, and is stable on the rising edge of CLK.
DOUT is high impedance except during MAX6960 read
accesses. Multiple MAX6960s may be connected to the
same 4-wire interface, with all devices connected to all
four interface lines in parallel. The normal limit of paral-
leled MAX6960s is 256, because that is the intercon-
nection limit for the 3-wire interface and associated
device addressing. The Applications Information sec-
tion discusses some practical issues raised by driving
many devices in parallel from the same interface.

The serial interface responds to only 8-bit, 16-bit, and
24-bit commands (Table 7).

The MAX6960 ignores any transmission that is not
exactly 8 bits, 16 bits, or 24 bits between the falling
and subsequent rising edge of

CS.

Control and Operation Using the 4-Wire Interface

Controlling the MAX6960 requires sending an 8-bit, 16-
bit, or 24-bit word. The last byte, D7 through D0, is
always the data byte. Eight-bit accesses are write-only
accesses; 16-bit or 24-bit accesses are read or write
accesses, as determined by the MSB of the transmis-
sion, which is set for a read access; clear for a write. A
16-bit or 24-bit read involves transmitting 16 or 24 bits
to DIN, taking

CS high, and then reading back 8 bits

from DOUT. Only one MAX6960’s DOUT is enabled
from tri-state for readback. The selected MAX6960’s
DOUT normally returns to tri-state after the 8th falling
edge of CLK. However if

CS falls during the read

before the 8th falling edge of CLK, then the readback is
terminated and the selected MAX6960’s DOUT returns
to tri-state.

If a number of bits other than exactly 8 bits, 16 bits, or
24 bits are clocked into the MAX6960 between taking
CS low and taking CS high again, then that transmis-
sion is ignored.

Writing Device Registers

The MAX6960 is written to using the following
sequence (Figures 3, 4, and 5):

1) Take CLK low.

2) Take

CS low.

3) For an 8-bit transmission:

Clock 8 bits of data into DIN, D7 first to D0 last,
observing the setup and hold times.

For a 16-bit transmission:

Clock 16 bits of data into DIN, D15 first to D0 last,

Dn-1

CSS

CSH

CSW

CLK

DIN

DOUT

Figure 5. Timing Diagram