CDP1020 Просмотр технического описания (PDF) - Intersil

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CDP1020

SMBus/I2C ACPI Dual Device Bay Controller

Intersil 

CDP1020

Hardware Interface

The hardware interface of the CDP1020 is designed to be fully

compliant with the Device Bay specification 0.90 and includes

many optional and value-added features that reduce system

component count, system complexity and overall system cost.

CLK Input

As stated at the beginning of this document, the Clock input

(CLK) provides the basic time base reference for operation of

all CDP1020 control logic (SMBus transfers between the

CDP1020 and the SMBus Host controller are not based on the

clock input). The clock input of the CDP1020 has the circuitry

necessary for oscillating an external resistor-capacitor circuit,

as shown in Figure 10. External clock sources (like those from

a can oscillator) should not be used with the CDP1020.

VDD = 5.0V

CLK 26

CDP1020

4.7kΩ

100pF

FIGURE 10. RC OSCILLATOR CONFIGURATION

The input frequency of the CDP1020 will vary for different

values of the oscillator resistor, the oscillator capacitor and

VDD. The CDP1020 is designed to operate optimally with an

input frequency of 4MHz. All of the internal timing of the

CDP1020, including debounce, insertion delay, and solenoid

pulse durations are based on a 4MHz input. While the

CDP1020 will operate at any frequency in the 3.0MHz to

5.0MHz range, an input frequency of 4MHz is strongly

recommended. Also, it is recommended that the value of the

oscillator capacitor be fixed at 100pF for optimal operation of

the oscillator.

Figure 11 shows a plot of oscillator frequency vs. resistance

at 5.0V and 3.3V when the oscillator capacitance is held

fixed at 100pF. Recommended values for the oscillator when

VDD = 5.0V are 4.7kΩ and 100pF; 3.3kΩ and 100pF when

VDD = 3.3V.

10

8

6

4

VDD = 5.0V

2

VDD = 3.3V

0

2.0

4.0

6.0

8.0

10.0

ROSC, OSCILLATOR RESISTOR (kΩ)

FIGURE 11. OSCILLATOR FREQUENCY vs ROSC (COSC = 100pF)

Presence Pins

The CDP1020 has two device presence detect inputs

(1394PRx and USBPRx) for each bay, for a total of four in all.

These inputs are mandatory in the Device Bay specification

and are the primary means of notifying the system that a

device has been inserted into a bay. Figure 18 shows a

typical connection of the CDP1020 presence pins.

The 1394 and USB presence lines are pulled up to the VDD of

the CDP1020 through active pull-up resistors located on the

CDP1020. These on chip resistors eliminate the need for

external pull-ups. Whenever any device is inserted into a bay,

that device must pull at least one (and possibly both) of the

presence pins to ground. Doing so indicates to the CDP1020

that a new device has been inserted and what communications

protocol it uses. Also, all presence pin inputs to the CDP1020

are debounced internally. The debounce time is set internally to

approximately 1 second to allow for transitions in the presence

pin state while the device is being inserted.

Typical current vs. voltage curves for the presence pin pull-

up resistor are shown in Figure 12. Pin assignments for

1394PR0, USBPR0, 1394PR1 and USBPR1 are shown on

the cover page and in Figure 2.

300

250

VDD = 5.0V

200

150

100 VDD = 3.3V

50

0

1.0 2.0 3.0 4.0 5.0 6.0

VI, INPUT VOLTAGE (V)

FIGURE 12. TYPICAL ACTIVE PULL-UP CURRENT AT 25oC

Remove Request (REMREQ) Inputs

The REMREQ inputs connect to an external, panel mounted

push button that allows the user to request removal of a

device. The implementation of the REMREQ feature is an

optional but encouraged feature of Device Bay specification

0.90. Each bay is assigned its own unique REMREQ input, as

such the CDP1020 implements REMREQ0 and REMREQ1.

Typical connection to a push button is shown in Figure 18.

The REMREQ inputs, like the presence pins, incorporate

integrated internal active pull-up devices. This allows the

system designer to implement the push button as a simple

momentary-on switch that pulls the input to ground when

pressed. When pressed, the CDP1020 will debounce the

switch press internally. No external pull-up resistors or

lowpass debounce filters are necessary.

2-437

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