MPC555 / MPC556
EXTERNAL BUS INTERFACE
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
9-1
SECTION 9
EXTERNAL BUS INTERFACE
The MPC555 / MPC556 bus is a synchronous, burstable bus. Signals driven on this
bus are required to make the setup and hold time relative to the bus clock’s rising
edge. The bus has the ability to support multiple masters. The MPC555 / MPC556 ar-
chitecture supports byte, half-word, and word operands allowing access to 8-, 16-, and
32-bit data ports through the use of synchronous cycles controlled by the size outputs
(TSIZ0, TSIZ1). For accesses to 16- and 8-bit ports, the slave must be controlled by
the memory controller.
9.1 Features
The external bus interface features are listed below.
• 32-bit address bus with transfer size indication (only 24 available on pins)
• 32-bit data bus
• Bus arbitration logic on-chip supports an external master
• Internal chip-select and wait state generation to support peripheral or static mem-
ory devices through the memory controller
• Supports various memory (SRAM, EEPROM) types: synchronous and asynchro-
nous, burstable and non-burstable
• Supports non-wrap bursts
• Flash ROM programming support
• Compatible with PowerPC architecture
• Easy to interface to slave devices
• Bus is synchronous (all signals are referenced to rising edge of bus clock)
• Bus can operate at the same frequency as the MPC555 / MPC556 or half the fre-
quency.
9.2 Bus Transfer Signals
The bus transfers information between the MPC555 / MPC556 and external memory
of a peripheral device. External devices can accept or provide 8, 16, and 32 bits in par-
allel and must follow the handshake protocol described in this section. The maximum
number of bits accepted or provided during a bus transfer is defined as the port width.
The MPC555 / MPC556 contains an address bus that specifies the address for the
transfer and a data bus that transfers the data. Control signals indicate the beginning
and type of the cycle, as well as the address space and size of the transfer. The se-
lected device then controls the length of the cycle with the signal(s) used to terminate
the cycle. A strobe signal for the address bus indicates the validity of the address and
provides timing information for the data.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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