Micrel, Inc.
UART mode
There are two UART modes of operation:
•
Direct UART:
-
UART TX SE0_VM_TX pin, data is output on D-
-
UART RX DAT_VP_RX pin receives UART data from
D+.
MIC2555
Suspend power:
The differential transmitter and receiver are turned off to
conserve power but the USB interface is still active (i.e.,
pull-ups and pull-downs still active, V
BUS
generation on,
etc.).
Conditions:
suspend = 1
pwr_dn = 0
Power Down:
Only the serial interface is still active and the transceiver
is able to detect SRP. The ID pin sensing may be turned
on or off with a control bit in the control registers.
Conditions:
suspend = 1
pwr_dn = 1
Functions Powered Down
By Control Bit
Differential Driver
Differential Receiver
UART TXD
D+ interrupt comparators
V
BUS
Comparators
V
TRM
LDO
V
BUS
output
Internal biasing circuits and
band gap reference
Charge Pump off
•
Secondary UART:
-
UART TX GPIO_1_TX pin, data is output on D-
-
UART RX GPOI_0_RX pin, received from D+.
Conditions for UART mode:
uart_en = 1
speed = 1
uart_io =
Direct UART = 0
Secondary UART inputs (GPIO) = 1
Note:
It is not necessary to reset uart_io when switching from
UART to USB mode; uart_io is deactivated when
uart_en = 0, so its setting will not effect DAT_VP_RX or
SE0_VM_TX’s operation in USB mode.
Audio Mode
There is one mode of Audio operation. In audio mode,
the MIC2555’s D+ and D- outputs are Tri-Stated (high
impedance) and the OTG controller or system
components can send and receive audio signals via the
D+, D- lines. The MIC2555 will monitor the D+ line for
voltages crossing one of two levels, as a means of
detecting a car kit interrupt signal. These interrupt events
are captured and flagged by the Serial Controller.
Conditions:
uart_en = 0
OE_INT/ = 1
cr_int_sel = detect
@
3.0V = 1
detect
@
0.5V = 0
Note:
The MIC2555 has no provision to connect or disconnect
audio devices from the D+, D- lines, so the designer is
cautioned to be sure that when the MIC2555 is operating
as a data transceiver, no damage will ensue if the
system’s audio components are exposed to USB or
UART digital signal levels.
Power Management
The transceiver’s power modes are:
Active power:
All functions active, transceiver fully powered.
Conditions:
suspend = 0
pwr_dn = 0
December 2006
Control Bit
suspend
●
●
●
●
●
●
●
●
●
●
pwr_dn
cp_off
Power Management Table
Note: Suspend and Power-Down bits operate
independently of each other. Activating Power-Down
does not automatically invoke Suspend.
For lowest power operation Suspend, Power-Down and
Charge Pump OFF modes must be activated:
Conditions:
suspend = 1
pwr_dn = 1
cp_off = 1
Circuits still operating:
ID detect and D- receiver continue to function.
This includes the ID comparators, ID pull-up
circuits, and D- data receiver.
11
M9999-121406
MICREL [ MICREL SEMICONDUCTOR ]
