Serial peripheral interface (spi) description – Rainbow Electronics ISD4004 User Manual
Page 9
ISD4004 Series
5
ISD
SERIAL PERIPHERAL INTERFACE (SPI) DESCRIPTION
The ISD4004 series operates from an SPI serial inter-
face. The SPI interface operates with the following
protocol.
The data transfer protocol assumes that the mi-
crocontroller’s SPI shift registers are clocked on the
falling edge of the SCLK. With the ISD4004, data is
clocked in on the MOSI pin on the rising clock
edge. Data is clocked out on the MISO pin on the
falling clock edge.
1. All serial data transfers begin with the falling
edge of SS pin.
2. SS is held LOW during all serial communica-
tions and held HIGH between instructions.
3. Data is clocked in on the rising clock edge
and data is clocked out on the falling clock
edge.
4. Play and Record operations are initiated by
enabling the device by asserting the SS pin
LOW, shifting in an opcode and an address
field to the ISD4004 device (refer to the Op-
code Summary on the page 6).
5. The opcodes and address fields are as fol-
lows: <8 control bits> and <16 address
bits>.
6. Each operation that ends in an EOM or
Overflow will generate an interrupt, includ-
ing the Message Cueing cycles. The Inter-
rupt will be cleared the next time an SPI
cycle is initiated.
7. As Interrupt data is shifted out of the
ISD4004 MISO pin, control and address
data is simultaneously being shifted into
the MOSI pin. Care should be taken such
that the data shifted in is compatible with
current system operation. It is possible to
read interrupt data and start a new opera-
tion within the same SPI cycle.
8. An operation begins with the RUN bit set
and ends with the RUN bit reset.
9. All operations begin with the rising edge
of SS.
MESSAGE CUEING
Message cueing allows the user to skip through
messages, without knowing the actual physical lo-
cation of the message. This operation is used dur-
ing playback. In this mode, the messages are
skipped 1600 times faster than in normal play-
back mode. It will stop when an EOM marker is
reached. Then, the internal address counter will
point to the next message.