Synchronous Serial Port
LH79524/LH79525 User’s Guide
14-2
Version 1.0
Table 14-1 describes these modes.
For all three formats, the serial clock (SSPCLK) is held inactive while the SSP is idle and
transitions at the programmed frequency only during active transmission of data. The
SSPCLK pin can be HIGH during idle in SPI Mode if the SPO bit in the Control Register is set.
For Motorola SPI and National Semiconductor Microwire frame formats, the serial frame
(SSPFRM) pin is active LOW and asserted (pulled down) during the entire frame transmis-
sion. Both formats output data on the falling edge of the clock and latch input data on the
rising edge of the clock.
Table 14-1. Feature Comparison
MODE
DESCRIPTION
DATA TRANSFERS
COMMENT
SPI
Lets the SSP communicate
with Motorola SPI-compatible
devices.
Full-duplex, 4-wire
synchronous
Clock polarity and phase
are programmable.
SSI
Lets the SSP communicate
with Texas Instruments DSP-
compatible Serial Synchronous
Interface devices.
Full-duplex, 4-wire
synchronous
Microwire
Lets the SSP communicate
with National Semiconductor
Microwire-compatible devices.
Half-duplex synchronous,
using 8-bit control
messages