The MAX3421E adds USB host or peripheral operation to any system with an SPI™ port.
The MAX3421E is a USB controller that can function either as a USB peripheral or host. It builds on Maxim's MAX3420E peripheral-only controller, and features an SPI interface that can run up to 26MHz. The MAX3421E contains a full-/low-speed transceiver, a smart serial interface engine (SIE), and a register file accessible through an SPI interface.
No. Like the MAX3420E, the MAX3421E is designed to work with any controller, such as a microcontroller, DSP, or ASIC. It connects to an SPI master that can run up to 26MHz.
Not entirely. The MAX3421E is a dual-role (peripheral and host) USB controller, so it implements the digital portion of OTG. Although it does not contain VBUS control and other analog details required by an OTG device, these functions can be added with external circuitry and controlled by the MAX3421E general-purpose IO pins.
SIE stands for Serial Interface Engine. The SIE converts signals received and sent by the USB transceiver into packets. An ordinary SIE does basic signal housekeeping, such as:
A smart SIE delves deeper into the USB protocol, handling higherlevel protocol issues so the programmer does not need to bother with them.
Here is an example. When a USB host sends an IN request to a peripheral and receives valid data but the wrong data toggle, what should the host do? A normal SIE would present the results (good data, bad toggle) to the microprocessor, and leave it to the firmware to respond correctly, according to the 622-page USB spec.
Here is what the MAX3421E's smart SIE does. The MAX3421E sends an ACK handshake, but does not complement its own data toggle or generate the interrupt request RCVDAV (Receive Data Available) which would indicate to the CPU that the received data is valid. If ACKing a packet with a bad toggle value sounds counter-intuitive, please review the MAX3421E Programming Guide for more details. The MAX3421E handles this part of the USB protocol so the firmware does not have to.
For another example, as a host the MAX3421E's smart SIE automatically generates 1 millisecond frame markers. The CPU connected to the MAX3421E launches host packets by writing a register called HXFR. If the CPU writes the HXFR register late in a frame and there is not enough time in the frame to avoid collision with the frame marker, the SIE automatically defers the sending transfer until the next frame.
Both devices have two voltage pins, VCC and VL. VL serves as the threshold voltage for the on-chip level translators, which allow the parts to operate in mixed-voltage systems.
If you compare the two supply currents, ICC and IL, for the two parts, you see that they differ because:
No. The MAX3421 has more signal pins than the MAX3420E, and the MAX3421E TQFP package (5mm by 5mm) is smaller than the MAX3420E TQFP package (7mm by 7mm).
Yes. When the MAX3421E powers on or is reset, it defaults to peripheral mode with the same register set as the MAX3420E.
The MAX3421E operates as a low-speed (1.5Mbps) or full-speed (12Mbps) host. At low speed, it supports CONTROL, BULK, and INTERRUPT transfers. At full-speed it supports CONTROL, BULK, INTERRUPT, and ISOCHRONOUS transfers.
Yes. The smart SIE manages the signaling details. If the host firmware sets a bit called HUBPRE to 1, the SIE automatically sends the full-speed PRE packet to the hub before reverting to low-speed signaling to the device.
Yes. If the design includes both an A and B USB connector, put the MAX3421E into host mode (HOST bit equals 1), switch on the internal DP/DM pulldown resistors, and supply 5V to the A-connector VBUS pin. A MAX3421E interrupt signals that a device is attaching. On the B-connector, connect the VBUS pin to the MAX3421E VBCOMP (VBUS Comparator) input. Then when the user connects to a PC, the MAX3421E detects VBUS and the MAX3421E configures as a peripheral.
Yes. The MAX3421E's SPI interface is identical to the MAX3420E's SPI interface. Please review Section 3 of the MAX3420E application note, Frequently Asked Questions about the MAX3420E on this subject.
Refer to the USB software download page, for the latest software downloads.
Yes, as a peripheral. Host certification is a relatively new USB testing concept, and Maxim intends to certify the MAX3421E as a USB host. You can check the Maxim web site for updates on USB certification, or sign up for automatic updates by email as they become available.
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