ST16C654CJ68 EXAR [Exar Corporation], ST16C654CJ68 Datasheet - Page 21

• Manufacturer Part Number: ST16C654CJ68
• Description: QUAD UART WITH 64-BYTE FIFO AND INFRARED (IrDA) ENCODER/DECODER
• Manufacturer: EXAR [Exar Corporation]

DMA Operation
The 654 FIFO trigger level provides additional flexibil-
ity to the user for block mode operation. LSR bits 5-6
provide an indication when the transmitter is empty or
has an empty location(s). The user can optionally
operate the transmit and receive FIFOs in the DMA
mode (FCR bit-3). When the transmit and receive
FIFOs are enabled and the DMA mode is deactivated
(DMA Mode “0”), the 654 activates the interrupt output
pin for each data transmit or receive operation. When
DMA mode is activated (DMA Mode “1”), the user
takes the advantage of block mode operation by
loading or unloading the FIFO in a block sequence
determined by the preset trigger level. In this mode,
the 654 sets the interrupt output pin when characters
in the transmit FIFOs are below the transmit trigger
level, or the characters in the receive FIFOs are above
the receive trigger level.
Sleep Mode
The 654 is designed to operate with low power con-
sumption. A special sleep mode is included to further
reduce power consumption when the chip is not being
used. With EFR bit-4 and IER bit-4 enabled (set to a
logic 1), the 654 enters the sleep mode but resumes
normal operation when a start bit is detected, a change
of state on any of the modem input pins RX, -RI, -CTS,
-DSR, -CD, or transmit data is provided by the user. If
the sleep mode is enabled and the 654 is awakened by
one of the conditions described above, it will return to
the sleep mode automatically after the last character
is transmitted or read by the user. In any case, the
sleep mode will not be entered while an interrupt(s) is
pending. The 654 will stay in the sleep mode of
operation until it is disabled by setting IER bit-4 to a
logic 0.
Rev. 4.10
5-85
Loopback Mode
The internal loopback capability allows onboard diag-
nostics. In the loopback mode the normal modem
interface pins are disconnected and reconfigured for
loopback internally. MCR register bits 0-3 are used for
controlling loopback diagnostic testing. In the
loopback mode OP1 and OP2 in the MCR register
(bits 3/2) control the modem -RI and -CD inputs
respectively. MCR signals -DTR and -RTS (bits 0-1)
are used to control the modem -CTS and -DSR inputs
respectively. The transmitter output (TX) and the
receiver input (RX) are disconnected from their asso-
ciated interface pins, and instead are connected to-
gether internally (See Figure 12). The -CTS, -DSR, -
CD, and -RI are disconnected from their normal
modem control inputs pins, and instead are connected
internally to -DTR, -RTS, -OP1 and -OP2. Loopback
test data is entered into the transmit holding register
via the user data bus interface, D0-D7. The transmit
UART serializes the data and passes the serial data to
the receive UART via the internal loopback connec-
tion. The receive UART converts the serial data back
into parallel data that is then made available at the
user data interface, D0-D7. The user optionally com-
pares the received data to the initial transmitted data
for verifying error free operation of the UART TX/RX
circuits.
In this mode, the receiver and transmitter interrupts
are fully operational. The Modem Control Interrupts
are also operational. However, the interrupts can only
be read using lower four bits of the Modem Control
Register (MCR bits 0-3) instead of the four Modem
Status Register bits 4-7. The interrupts are still con-
trolled by the IER.
ST16C654/654D