Full-speed Universal Serial Bus peripheral controller
Rev. 02 — 07 December 2004Product data
1.General description
The ISP1181B is a Universal Serial Bus (USB) peripheral controller that complies
with
UniversalSerial Bus Specification Rev. 2.0
(12 Mbit/s). It provides full-speed USB communication capacity to microcontroller or
microprocessor-based systems. The ISP1181B communicates with the system’s
microcontroller or microprocessor through a high-speed general-purpose parallel
interface.
The ISP1181B supports fully autonomous, multi-configurable Direct Memory Access
(DMA) operation.
The modular approach to implementing a USB peripheral controller allows the
designer to select the optimum system microcontrollerfrom the wide variety available.
The ability to reuse existing architecture and firmware investments shortens
development time, eliminates risks and reduces costs. The result is fast and efficient
development of the most cost-effective USB peripheral solution.
, supporting data transferat full-speed
2.Features
The ISP1181B is ideally suited forapplication in many personal computer peripherals
such as printers, communication devices, scanners, external mass storage (Zip
drive) devices and digital still cameras. It offers an immediate cost reduction for
applications that currently use SCSI implementations.
■ Complies with
specifications
■ Supports data transfer at full-speed (12 Mbit/s)
■ High performance USB peripheral controller with integrated Serial Interface
Engine (SIE), FIFO memory, transceiver and 3.3 V voltage regulator
■ High speed (11.1 Mbyte/s or 90 ns read/write cycle) parallel interface
■ Fully autonomous and multi-configuration DMA operation
■ Up to 14 programmable USB endpoints with 2 fixed control IN/OUT endpoints
■ Integrated physical 2462 bytes of multi-configuration FIFO memory
■ Endpoints with double buffering to increase throughput and ease real-time data
transfer
■ Seamless interface with most microcontrollers/microprocessors
■ Bus-powered capability with low power consumption and low ‘suspend’ current
■ 6 MHz crystal oscillator input with integrated PLL for low EMI
polarity, see Table 21); used by the DMA
controller to force the end of a DMA transfer
to the ISP1181B
DREQ116ODMA request output (4 mA; programmable
polarity, see Table 21); signals to the DMA
controller that the ISP1181B wants to start
a DMA transfer
DACK127IDMA acknowledge input (programmable
polarity, see Table 21); used by the DMA
controller to signal the start of a DMA
transfer requested by the ISP1181B
TEST1138Itest input; this pin must be connected to
via an external 10 kΩ resistor
V
CC
TEST2149Itest input; this pin must be connected to
via an external 10 kΩ resistor
V
CC
INT1510Ointerrupt output; programmable polarity
(active HIGH or LOW) and signalling (level
or pulse); see Table 21
TEST31611Otest output; this pin is used for test
purposes only
BUS_CONF01712Ibus configuration selector; see Table 3
BUS_CONF11813Ibus configuration selector; see Table 3
DATA151914I/Obit 15 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
DATA142015I/Obit 14 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
DATA132116I/Obit 13 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
DATA122217I/Obit 12 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
DATA112318I/Obit 11 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
DATA102419I/Obit 10 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
GND2520-ground supply
V
ref
2621-I/O pin reference voltage (3.3 V); no
connection if V
CC
= 5.0 V
DATA92722I/Obit 9 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
DATA82823I/Obit 8 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
DATA72924I/Obit 7 of D[15:0]; bidirectional data line
(slew-rate controlled output, 4 mA)
DATA63025I/Obit 6 of D[15:0]; bidirectional data line
The ISP1181B is a full-speed USB peripheral controller with up to 14 configurable
endpoints. It has a fast general-purpose parallel interface for communication with
many types of microcontrollers or microprocessors. It supports different bus
configurations (see Table 3) and local DMA transfers of up to 16 bytes per cycle. The
block diagram is given in Figure 1.
The ISP1181B has 2462 bytes of internal FIFO memory, which is shared among the
enabled USB endpoints. The type and FIFO size of each endpoint can be individually
configured, depending on the required packet size. Isochronous and bulk endpoints
are double-buffered for increased data throughput.
The ISP1181B requires a single supply voltage of 3.3 V or 5.0 V and has an internal
3.3 V voltage regulator for powering the analog USB transceiver. It supports
bus-powered operation.
The ISP1181B operates on a 6 MHz oscillator frequency. A programmable clock
output is available up to 48 MHz. During ‘suspend’ state the 100 kHz ± 50 %
LazyClock frequency can be output.
ISP1181B
Full-speed USB peripheral controller
7.1 Analog transceiver
The transceiver is compliant with the
speed)
resistors.
. It interfaces directly with the USB cable through external termination
Universal Serial Bus Specification Rev. 2.0 (full
7.2 Philips Serial Interface Engine (SIE)
The Philips SIE implements the full USB protocol layer. It is completely hardwired for
speed and needs no firmware intervention. The functions of this block include:
synchronization pattern recognition, parallel/serial conversion, bit (de-)stuffing, CRC
checking/generation, Packet IDentifier (PID) verification/generation, address
recognition, handshake evaluation/generation.
7.3 Memory Management Unit (MMU) and integrated RAM
The MMU and the integrated RAM provide the conversion between the USB speed
(12 Mbit/s bursts) and the parallel interface to the microcontroller (max. 12 Mbyte/s).
This allows the microcontroller to read and write USB packets at its own speed.
7.4 SoftConnect
The connection to the USB is accomplished by bringing D+ (for full-speed USB
peripherals) HIGH through a 1.5 kΩ pull-up resistor. In the ISP1181B, the 1.5 kΩ
pull-up resistor is integrated on-chip and is not connected to VCC by default. The
connection is established by a command sent from the external/system
microcontroller. This allows the system microcontroller to complete its initialization
sequence before deciding to establishconnection with the USB. Reinitialization of the
USB connection can also be performed without disconnecting the cable.
Without V
With V
there is noise on the (D+, D-) lines, it is not taken into account. This ensures that the
peripheral remains in the suspend state.
Remark: Note that the tolerance of the internal resistors is 25 %. This is higher than
the 5 % tolerance specified by the USB specification. However, the overall voltage
specification for the connection can still be met with a good margin. The decision to
make use of this feature lies with the USB equipment designer.
7.5 GoodLink
Indication of a good USB connection is provided at pin GL through GoodLink
technology. During enumeration, the LED indicator will blink on momentarily. When
the ISP1181B has been successfully enumerated (the peripheral address is set), the
LED indicator will remain permanently on. Upon each successful packettransfer(with
ACK) to and from the ISP1181B, the LED will blink off for 100 ms. During ‘suspend’
state, the LED will remain off.
Full-speed USB peripheral controller
sensing prevents the peripheral from wake-up when V
sensing, any activity or noise on (D+, D-) might wake up the peripheral.
BUS
sensing, (D+, D-) is decoupled when no V
BUS
is present. Therefore, even if
BUS
ISP1181B
is not present.
BUS
This feature provides a user-friendly indication of the status of the USB peripheral,
the connected hub,and the USB traffic. It is a useful field diagnostics tool forisolating
faulty equipment. It can therefore help to reduce field support and hotline overhead.
7.6 Bit clock recovery
The bit clock recovery circuit recovers the clock from the incoming USB data stream
using a 4 times over-sampling principle. It is able to track jitter and frequency drift as
specified by the
USB Specification Rev. 2.0
.
7.7 Voltage regulator
A 5 V-to-3.3 V voltage regulator is integrated on-chip to supply the analog transceiver
and internal logic. This voltage is availableat pin V
to supply an external 1.5 kΩ
reg(3.3)
pull-up resistor on the D+ line. Alternatively, the ISP1181B provides SoftConnect
technology via an integrated 1.5 kΩ pull-up resistor (see Section 7.4).
7.8 PLL clock multiplier
A 6 MHz to 48 MHz clock multiplier Phase-Locked Loop (PLL) is integrated on-chip.
This allows for the use of a low-cost 6 MHz crystal, which also minimizes EMI. No
external components are required for the operation of the PLL.
7.9 Parallel I/O (PIO) and Direct Memory Access (DMA) interface
A generic PIO interface is defined for speed and ease-of-use. It also allows direct
interfacing to most microcontrollers. To a microcontroller, the ISP1181B appears as a
memory device with an 8/16-bit data bus and a 1-bit address line. The ISP1181B
supports both multiplexed and non-multiplexed address and data buses.
The ISP1181B can also be configured as a DMA slave device to allow more efficient
data transfer. One of the 14 endpoint FIFOs may directly transfer data to/from the
local shared memory. The DMA interface can be configured independently from the
PIO interface.
The ISP1181B has fourbusconfiguration modes, selected via pins BUS_CONF1 and
BUS_CONF0:
Mode 016-bit I/O port shared with 16-bit DMA port
Mode 1reserved
Mode 28-bit I/O port shared with 8-bit DMA port
Mode 3reserved.
The bus configurations foreach of these modes are given in Table 3. Typical interface
circuits for each mode are given in Section 22.1.
Table 3:Bus configuration modes
ModeBUS_CONF[1:0]PIO widthDMA widthDescription
DMAWD = 0DMAWD = 1
000D[15:1], AD0-D[15:1], AD0multiplexed address/data on pin AD0;
bus is shared by 16-bit I/O port and
16-bit DMA port
101reservedreservedreservedreserved
210D[7:1], AD0D[7:1], AD0-multiplexed address/data on pin AD0;
bus is shared by 8-bit I/O port and 8-bit
DMA port
311reservedreservedreservedreserved
9.Endpoint descriptions
Each USB peripheral is logically composed of several independent endpoints. An
endpoint acts as a terminus of a communication flow between the host and the
peripheral. At design time each endpoint is assigned a unique number (endpoint
identifier, see Table 4). The combination of the peripheral address (given by the host
during enumeration), the endpoint number and the transfer direction allows each
endpoint to be uniquely referenced.
The ISP1181B has 16 endpoints: endpoint 0 (control IN and OUT) plus 14
configurable endpoints, which can be individually defined as
interrupt/bulk/isochronous, IN or OUT. Each enabled endpoint has an associated
FIFO, which can be accessed either via the parallel I/O interface or via DMA.
9.1 Endpoint access
Table 4 lists the endpoint access modes and programmability. All endpoints support
I/O mode access. Endpoints 1 to 14 also support DMA access. FIFO DMA access is
selected and enabled via bits EPIDX[3:0] and DMAEN of the DMA Configuration
Register. A detailed description of the DMA operation is given in Section 10.
064 (fixed)noyesnocontrol OUT
064 (fixed)noyesnocontrol IN
1programmablesupportedsupportedsupportedprogrammable
2programmablesupportedsupportedsupportedprogrammable
3programmablesupportedsupportedsupportedprogrammable
4programmablesupportedsupportedsupportedprogrammable
5programmablesupportedsupportedsupportedprogrammable
6programmablesupportedsupportedsupportedprogrammable
7programmablesupportedsupportedsupportedprogrammable
8programmablesupportedsupportedsupportedprogrammable
9programmablesupportedsupportedsupportedprogrammable
10programmablesupportedsupportedsupportedprogrammable
11programmablesupportedsupportedsupportedprogrammable
12programmablesupportedsupportedsupportedprogrammable
13programmablesupportedsupportedsupportedprogrammable
14programmablesupportedsupportedsupportedprogrammable
FIFO size (bytes)
[1]
Double
buffering
I/O mode
access
DMA mode
access
Endpoint type
[2]
[2]
[1] The total amount of FIFO storage allocated to enabled endpoints must not exceed 2462 bytes.
[2] IN: input for the USB host (ISP1181B transmits); OUT: output from the USB host (ISP1181B receives). The data flow direction is
determined by bit EPDIR in the Endpoint Configuration Register.
9.2 Endpoint FIFO size
The size of the FIFO determines the maximum packet size that the hardware can
support for a given endpoint. Only enabled endpoints are allocated space in the
shared FIFO storage, disabled endpoints have zero bytes. Table 5 lists the
programmable FIFO sizes.
The following bits in the Endpoint Configuration Register (ECR) affect FIFO
allocation:
• Endpoint enable bit (FIFOEN)
• Size bits of an enabled endpoint (FFOSZ[3:0])
• Isochronous bit of an enabled endpoint (FFOISO).
Remark: Register changes that affect the allocation of the shared FIFO storage
among endpoints must not be made while valid data is present in any FIFO of the
enabled endpoints. Such changes will render all FIFO contents undefined.
Each programmable FIFO can be configured independently via its ECR, but the total
physical size of all enabled endpoints (IN plus OUT) must not exceed 2462 bytes.
Table 6 showsan exampleof a configuration fitting in the maximumavailable space of
2462 bytes. The total number of logical bytes in the example is 1311. The physical
storage capacity used for double buffering is managed by the peripheral hardware
and is transparent to the user.
Table 6:Memory configuration example
Physical size
(bytes)
6464control IN (64 byte fixed)
6464control OUT (64 byte fixed)
20461023double-buffered 1023-byte isochronous endpoint
161616-byte interrupt OUT
161616-byte interrupt IN
12864double-buffered 64-byte bulk OUT
12864double-buffered 64-byte bulk IN
In response to the standard USB request, Set Interface, the firmware must program
all 16 ECRs of the ISP1181B in sequence (see Table 4), whether the endpoints are
enabled or not. The hardware will then automatically allocate FIFO storage space.
If all endpoints havebeen configured successfully, the firmware must return an empty
packet to the control IN endpoint to acknowledge success to the host. If there are
errors in the endpoint configuration, the firmware must stall the control IN endpoint.
When reset by hardware or via the USB bus, the ISP1181B disables all endpoints
and clears all ECRs, except for the control endpoint which is fixed and always
enabled.
Endpoint initialization can be done at any time; however, it is valid only after
enumeration.
9.4 Endpoint I/O mode access
When an endpoint event occurs (a packet is transmitted or received), the associated
endpoint interrupt bits (EPn) of the Interrupt Register (IR) will be set by the SIE. The
firmware then responds to the interrupt and selects the endpoint for processing.
ISP1181B
Full-speed USB peripheral controller
The endpoint interrupt bit will be cleared by reading the Endpoint Status Register
(ESR). The ESR also contains information on the status of the endpoint buffer.
For an OUT (= receive) endpoint, the packet length and packet data can be read from
ISP1181B using the Read Buffer command. When the whole packet has been read,
the firmware sends a Clear Buffer command to enable the reception of new packets.
For an IN (= transmit) endpoint, the packet length and data to be sent can be written
to ISP1181B using the Write Buffer command. When the whole packet has been
written to the buffer, the firmware sends a Validate Buffer command to enable data
transmission to the host.
9.5 Special actions on control endpoints
Control endpoints require special firmware actions. The arrival of a SETUP packet
flushes the IN bufferand disables the Validate Buffer and Clear Buffer commands for
the control IN and OUT endpoints. The microcontroller needs to re-enable these
commands by sending an Acknowledge Setup command to both control endpoints.
This ensures that the last SETUP packet stays in the buffer and that no packets can
be sent back to the host until the microcontroller has explicitly acknowledged that it
has seen the SETUP packet.
Direct Memory Access (DMA) is a method to transfer data from one location to
another in a computer system, without intervention of the central processor (CPU).
Many different implementations of DMA exist. The ISP1181B supports two methods:
• 8237 compatible mode: based on the DMA subsystem of the IBM personal
• DACK-only mode: based on the DMA implementation in some embedded RISC
The ISP1181B supports DMA transfer for all 14 configurable endpoints (see Table 4).
Only one endpoint at a time can be selected for DMA transfer.The DMA operation of
the ISP1181B can be interleaved with normal I/O mode access to other endpoints.
The following features are supported:
• Single-cycle or burst transfers (up to 16 bytes per cycle)
• Programmable signal levels on pins DREQ, DACK and EOT.
ISP1181B
Full-speed USB peripheral controller
computers (PC, AT and all its successors and clones); this architecture uses the
Intel 8237 DMA controller and has separate address spaces for memory and I/O
processors, which has a single address space for both memory and I/O.
short/empty packet
10.1 Selecting an endpoint for DMA transfer
The target endpoint for DMA access is selected via bits EPDIX[3:0] in the DMA
Configuration Register, as shown in Table 7. The transfer direction (read or write) is
automatically set by bit EPDIR in the associated ECR, to match the selected endpoint
type (OUT endpoint: read; IN endpoint: write).
Asserting input DACK automatically selects the endpoint specified in the DMA
Configuration Register, regardless of the current endpoint used for I/O mode access.
The 8237 compatible DMA mode is selected by clearing bit DAKOLY in the Hardware
Configuration Register (see Table 20). The pin functions for this mode are shown in
Table 8.
Table 8:8237 compatible mode: pin functions
SymbolDescriptionI/OFunction
DREQDMA requestOISP1181B requests a DMA transfer
DACKDMA acknowledgeIDMA controller confirms the transfer
EOTend of transferIDMA controller terminates the transfer
RDread strobeIinstructs ISP1181B to put data on the bus
WRwrite strobeIinstructs ISP1181B to get data from the
…continued
EPDIR = 0EPDIR = 1
bus
The DMA subsystem of an IBM compatible PC is based on the Intel 8237 DMA
controller. It operates as a ‘fly-by’ DMA controller: the data is not stored in the DMA
controller, but it is transferred between an I/O port and a memory address. A typical
example of ISP1181B in 8237 compatible DMA mode is given in Figure 4.
The 8237 has two control signals for each DMA channel: DREQ (DMA Request) and
DACK (DMA Acknowledge). General control signals are HRQ (Hold Request) and
HLDA (Hold Acknowledge). The bus operation is controlled via MEMR (Memory
Read), MEMW (Memory Write), IOR (I/O read) and IOW (I/O write).
The following example shows the steps which occur in a typical DMA transfer:
1. ISP1181B receives a data packet in one of its endpoint FIFOs; the packet must
2. ISP1181B asserts the DREQ signal requesting the 8237 for a DMA transfer.
3. The 8237 asks the CPU to release the bus by asserting the HRQ signal.
4. After completing the current instruction cycle, the CPU places the bus control
5. The 8237 now sets its address lines to 1234H and activates the MEMW and IOR
6. The 8237 asserts DACK to inform the ISP1181B that it will start a DMA transfer.
7. The ISP1181B now places the byte or word to be transferred on the data bus
8. The8237waits one DMA clock period and then de-asserts MEMW and IOR. This
9. The ISP1181B de-asserts the DREQ signal to indicate to the 8237 that DMA is
10. The 8237 de-asserts the DACK output indicating that the ISP1181B must stop
11. The 8237 places the bus control signals (MEMR, MEMW, IOR and IOW) and the
12. The CPU acknowledges control of the bus by de-asserting HLDA. After activating
ISP1181B
Full-speed USB peripheral controller
be transferred to memory address 1234H.
signals (MEMR, MEMW, IOR and IOW) and the address lines in three-state and
asserts HLDA to inform the 8237 that it has control of the bus.
control signals.
lines, because its RD signal was asserted by the 8237.
latches and stores the byte or word at the desired memory location. It also
informs the ISP1181B that the data on the bus lines has been transferred.
no longer needed. In Single cycle mode this is done after each byte or word, in
Burst mode following the last transferred byte or word of the DMA cycle.
placing data on the bus.
address lines in three-state and de-asserts the HRQ signal, informing the CPU
that it has released the bus.
the bus control lines (MEMR, MEMW, IOR and IOW) and the address lines, the
CPU resumes the execution of instructions.
Fora typical bulk transfer the above process is repeated 64 times, once for each byte.
After each byte the address register in the DMA controller is incremented and the
byte counter is decremented. When using 16-bit DMA, the number of transfers is 32
and address incrementing and byte counter decrementing is done by 2 for each word.
10.3 DACK-only mode
The DACK-only DMA mode is selected by setting bit DAKOLY in the Hardware
Configuration Register (see Table 20). The pin functions for this mode are shown in
Table 9.Atypical exampleof ISP1181B in DACK-onlyDMA mode is given in Figure 5.
Table 9:DACK-only mode: pin functions
SymbolDescriptionI/OFunction
DREQDMA requestOISP1181B requests a DMA transfer
DACKDMA acknowledgeIDMA controller confirms the transfer;
also functions as data strobe
EOTEnd-Of-TransferIDMA controller terminates the transfer
RDread strobeInot used
WRwrite strobeInot used
In DACK-only mode the ISP1181B uses the DACK signal as data strobe. Input
signals RD and WR are ignored. This mode is used in CPU systems that have a
single address space for memory and I/O access. Such systems have no separate
MEMW and MEMR signals: the RD and WR signals are also used as memory data
strobes.
ISP1181B
Full-speed USB peripheral controller
ISP1181BDMA
DREQ
DACK
AD0,
DATA1 to DATA15
Fig 5. ISP1181B in DACK-only DMA mode.
10.4 End-Of-Transfer conditions
10.4.1 Bulk endpoints
A DMA transfer to/from a bulk endpoint can be terminated by any of the following
conditions (bit names refer to the DMA Configuration Register, see Table 24):
• An external End-Of-Transfer signal occurs on input EOT
• The DMA transfer completes as programmed in the DMA Counter register
(CNTREN = 1)
• A short packet is received on an enabled OUT endpoint (SHORTP = 1)
• DMA operation is disabled by clearing bit DMAEN.
RAM
CONTROLLER
DREQ
DACK
RD
WR
HRQ
HLDA
CPU
HRQ
HLDA
004aaa138
External EOT: When reading from an OUT endpoint, an external EOT will stop the
DMA operation and clear any remaining data in the current FIFO. For a doublebuffered endpoint the other (inactive) buffer is not affected.
When writing to an IN endpoint, an EOT will stop the DMA operation and the data
packet in the FIFO (evenif it is smaller than the maximum packet size) will be sent to
the USB host at the next IN token.
DMA Counter Register: An EOT from the DMA Counter Register is enabled by
setting bit CNTREN in the DMA Configuration Register. The ISP1181B has a 16-bit
DMA Counter Register, which specifies the number of bytes to be transferred. When
DMA is enabled (DMAEN = 1), the internal DMA counter is loaded with the value from
the DMA Counter Register. When the internal counter completes the transfer as
programmed in the DMA counter, an EOT condition is generated and the DMA
operation stops.
Short packet: Normally, the transfer byte count must be set via a control endpoint
before any DMA transfer takes place. When a short packet has been enabled as EOT
indicator (SHORTP = 1), the transfer size is determined by the presence of a short
packet in the data. This mechanism permits the use of a fully autonomous data
transfer protocol.
When reading from an OUT endpoint, reception of a short packet at an OUT token
will stop the DMA operation after transferring the data bytes of this packet.
Table 10: Summary of EOT conditions for a bulk endpoint
EOT conditionOUT endpointIN endpoint
EOT inputEOT is activeEOT is active
DMA Counter Registertransfer completes as
Short packetshort packet is received and
DMAEN bit in DMA
Configuration Register
Full-speed USB peripheral controller
programmed in the DMA
Counter register
transferred
DMAEN = 0
[1]
ISP1181B
transfer completes as
programmed in the DMA
Counter register
counter reaches zero in the
middle of the buffer
DMAEN = 0
[1]
[1] The DMA transfer stops. However, no interrupt is generated.
10.4.2 Isochronous endpoints
A DMA transfer to/from an isochronous endpoint can be terminated by any of the
following conditions (bit names refer to the DMA Configuration Register, see
Table 24):
• An external End-Of-Transfer signal occurs on input EOT
• The DMA transfer completes as programmed in the DMA Counter register
(CNTREN = 1)
• An End-Of-Packet (EOP) signal is detected
• DMA operation is disabled by clearing bit DMAEN.
Table 11: Recommended EOT usage for isochronous endpoints
EOT conditionOUT endpointIN endpoint
EOT input activedo not usepreferred
DMA Counter Register zerodo not usepreferred
End-Of-Packetpreferreddo not use
The ISP1181B detects a USB suspend status when a constant idle state is present
on the USB bus for more than 3 ms.
The bus-powered devices that are suspended must not consume more than 500 µA
of current. This is achieved by shutting down power to system components or
supplying them with a reduced voltage.
The steps leading up to suspend status are as follows:
1. Ondetecting a wake-up-to-suspend transition, the ISP1181B sets bit SUSPND in
the Interrupt register. This will generate an interrupt if bit IESUSP in the Interrupt
Enable register is set.
2. When the firmware detects a suspend condition, it must prepare all system
components for the suspend state:
a. Allsignals connected to the ISP1181B must enter appropriate states to meet
the power consumption requirements of the suspend state.
b. All input pins of the ISP1181B must have a CMOS LOW or HIGH level.
3. In the interrupt service routine, the firmware must check the current status of the
USB bus. When bit BUSTATUS in the Interrupt register is logic 0, the USB bus
has left the suspend mode and the process must be aborted. Otherwise, the next
step can be executed.
4. To meet the suspend current requirements for a bus-powered device, the internal
clocks must be switched off by clearing bit CLKRUN in the Hardware
Configuration register.
5. When the firmware has set and cleared bit GOSUSP in the Mode register, the
ISP1181B enters the suspend state. In powered-off application, the ISP1181B
asserts output SUSPEND and switches off the internal clocks after 2 ms.
• A: indicates the point at which the USB bus enters the idle state.
• B: indicates resume condition, which can be a 20 ms K-state on the USB bus, a
HIGH level on pin WAKEUP, or a LOW level on pin CS.
• C: indicates remote wake-up. The ISP1181B will drive a K-state on the USB bus
for 10 ms after pin WAKEUP goes HIGH or pin CS goes LOW.
• D: after detecting the suspend interrupt, set and clear bit GOSUSP in the Mode
register.
11.1.1 Powered-off application
Figure 7 shows a typical bus-powered modem application using the ISP1181B. The
SUSPEND output switches off powerto the microcontroller and other external circuits
during the suspend state. The ISP1181B is woken up through the USB bus (global
resume) or by the ring detection circuit on the telephone line.