Signal Summary
MOTOROLA
ColdFire2/2M User’s Manual
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2-9
2.4.1.10 INSTRUCTION CACHE TAG OUTPUT BUS (ICHT_DO[31:8]).
signals provide the read data path between the cache tag RAM and the ColdFire2/2M. The
data bus is 24-bits wide. Bit eight is always the valid bit and is always used regardless of the
cache configuration as shown in
Table 2-8
. This bus should be connected to the data
outputs (DBO) of the compiled cache tag RAM. Unused signals must be tied low.
These input
2.4.1.11 INSTRUCTION CACHE TAG STROBE (ICHT_ST).
read or write cycle to the cache tag RAM on a low-to-high transition. This signal should be
connected to the strobe input (ST) signal of the compiled cache tag RAM.
This output signal initiates a
2.4.1.12 INSTRUCTION CACHE TAG READ/WRITE (ICHT_RWB).
indicates the direction of the data transfer to the cache tag RAM. A high level indicates a
read cycle and a low level indicates a write cycle. It should be connected to the read/write
(RWB) signal of the compiled cache tag RAM.
This output signal
2.4.2 Integrated ROM Signals
These signals interface the ColdFire2/2M to the optional integrated ROMs.
2.4.2.1 ROM ADDRESS BUS (ROM_ADDR[14:2]).
address of the current bus cycle to the integrated ROMs. This bus should be connected to
the address bus (A) of the compiled ROMs. The number of valid address signals depends
on the total ROM size as shown in
Table 2-9
.
These output signals provide the
2.4.2.2 ROM DATA OUTPUT BUS (ROM_DO[31:0]).
read data path from the integrated ROMs to the ColdFire2/2M. The data bus is 32-bits wide
and can transfer 8, 16, or 32 bits of data per bus transfer. During a line transfer, the data
lines are time-multiplexed across multiple cycles to carry 128 bits. This bus should be
connected to the data outputs (DO) of the compiled ROMs.
These input signals provide the
2.4.2.3 ROM ENABLE (ROM_ENB[1:0]).
ROMs are currently selected to drive the ROM_DO[31:0] bus. These signals should be
connected individually to the enable signal (ROMENB) signal of the compiled ROMs. Both
are asserted for 32-bit accesses. ROM_ENB[0] connects to the MSW while ROM_ENB[1]
connects to the LSW.
These active-low, output signals indicate the
Table 2-9. Valid ROM Address Bits
TOTAL ROM SIZE
0
512
1 K
2 K
4 K
8 K
16K
32K
VALID ROM_ADDR BITS
None
ROM_ADDR[8:2]
ROM_ADDR[9:2]
ROM_ADDR[10:2]
ROM_ADDR[11:2]
ROM_ADDR[12:2]
ROM_ADDR[13:2]
ROM_ADDR[14:2]
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