KSZ8842-MQL Datasheet, PDF (63/141 Pages) Micrel Semiconductor – 2-Port Ethernet Switch with Non-PCI Interface

Micrel, Inc.
KSZ8842-16/32 MQL/MVL/MVLI/MBL
Bank 3 On-Chip Bus Control Register (0x00): OBCR
This register controls the on-chip bus speed for the KSZ8842M. It is used for power management when the external host
CPU is running at a slow frequency. The default of the on-chip bus speed is 125 MHz without EEPROM. When the
external host CPU is running at a higher clock rate, the on-chip bus should be adjusted for the best performance.
Bit
15-2
1-0
Default Value R/W
-
RO
0x0
RW
Description
Reserved
OBSC On-Chip Bus Speed Control
00: 125MHz.
01: 62.5MHz.
10: 41.66MHz.
11: 25MHz.
Note: When external EEPROM is enabled, the bit 1 in Configparm word (0x6H) is
used to contol this speed as below:
Bit 1 = 0 , this value will be 00 for 125 MHz.
Bit 1 = 1 , this value will be 11 for 25 MHz.
(User still can write these two bits to change speed after EEPROM data loaded)
Bank 3 EEPROM Control Register (0x02): EEPCR
To support an external EEPROM, tie the EEPROM Enable (EEEN) pin to High; otherwise, tie it to Low. If an external
EEPROM is not used, the default chip Base Address (0x300), and the software programs the host MAC address. If an
EEPROM is used in the design (EEPROM Enable pin to High), the chip Base Address and host MAC address are loaded
from the EEPROM immediately after reset. The KSZ8842M allows the software to access (read and write) the EEPROM
directly; that is, the EEPROM access timing can be fully controlled by the software if the EEPROM Software Access bit is
set.
Bit
15-5
4
3
2-0
Default Value R/W
-
RO
0
RW
-
RO
0x0
RW
Description
Reserved
EESA EEPROM Software Access
1: enable software to access EEPROM through bit 3 to bit 0.
0: disable software to access EEPROM.
EECB EEPROM Status Bit
Data Receive from EEPROM. This bit directly reads the EEDI pin.
EECB EEPROM Control Bits
Bit 2: Data Transmit to EEPROM. This bit directly controls the device’s EEDO pin.
Bit 1: Serial Clock. This bit directly controls the device’s EESK pin.
Bit 0: Chip Select for EEPROM. This bit directly controls the device’s EECS pin.
October 2007
63
M9999-102207-1.9