ENC28J60
After a System Reset, all PHY registers should not be
read or written to until at least 50 μs have passed since
the Reset has ended. All registers will revert to their
Reset default values. The dual port buffer memory will
maintain state throughout the System Reset.
11.1 Power-on Reset (POR)
A
Power-on Reset pulse is generated on-chip
whenever VDD rises above a certain threshold. This
allows the device to start in the initialized state when
VDD is adequate for operation.
The POR circuitry is always enabled. As a result, most
applications do not need to attach any external circuitry
to the RESET pin to ensure a proper Reset at power-
up. The RESET pin’s internal weak pull-up will maintain
a logical high level on the pin during normal device
operation.
11.3 Transmit Only Reset
The Transmit Only Reset is performed by writing a ‘1’ to
the TXRST bit in the ECON1 register using the SPI inter-
face. If a packet was being transmitted when the TXRST
bit was set, the hardware will automatically clear the
TXRTS bit and abort the transmission. This action resets
the transmit logic only. The System Reset automatically
performs the Transmit Only Reset. Other register and
control blocks, such as buffer management and host
interface, are not affected by a Transmit Only Reset
event. When the host controller wishes to return to
normal operation, it should clear the TXRST bit.
To ensure proper POR operation, a minimum rise rate
for VDD is specified (parameter D003). The application
circuit must meet this requirement to allow the Oscillator
Start-up Timer and CLKOUT functions to reset properly.
After a Power-on Reset, the contents of the dual port
buffer memory will be unknown. However, all registers
will be loaded with their specified Reset values. Certain
portions of the ENC28J60 must not be accessed
immediately after a POR. See Section 2.2 “Oscillator
Start-up Timer” for more information.
11.4 Receive Only Reset
The Receive Only Reset is performed by writing a ‘1’ to
the RXRST bit in the ECON1 register using the SPI
interface. If packet reception was enabled (the RXEN
bit was set) when RXRST was set, the hardware will
automatically clear the RXEN bit. If a packet was being
received, it would be immediately aborted. This action
resets receive logic only. The System Reset automati-
cally performs Receive Only Reset. Other register and
control blocks, such as the buffer management and
host interface blocks, are not affected by a Receive
Only Reset event. When the host controller wishes to
return to normal operation, it should clear the RXRST
bit.
11.2 System Reset
The System Reset of ENC28J60 can be accomplished
by either the RESET pin, or through the SPI interface.
The RESET pin provides an asynchronous method for
triggering an external Reset of the device. A Reset is
generated by holding the RESET pin low. The
ENC28J60 has a noise filter in the RESET path which
detects and ignores small pulses of time tRSTLOW or
less. When the RESET pin is held high, the ENC28J60
will operate normally.
The ENC28J60 can also be reset via the SPI using the
System Reset Command. See Section 4.0 “Serial
Peripheral Interface (SPI)”.
The RESET pin will not be driven low by any internal
Resets, including a System Reset Command via the
SPI interface.
DS39662B-page 60
Preliminary
© 2006 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
