MPC555
/
MPC556
DUAL-PORT TPU RAM (DPTRAM)
MOTOROLA
USER’S MANUAL
Rev. 15 October 2000
18-5
18.3.3 Ram Base Address Register (RAMBAR)
The RAMBAR register is used to specify the 16 MSBs of the starting DPT RAM array
location in the memory map. In the MPC555 / MPC556, this register must be pro-
gramed to the value 0xFFA0.
This register can be written only once after a reset. This prevents runaway software
from inadvertently re-mapping the array. Since the locking mechanism is triggered by
the first write after reset, the base address of the array should be written in a single
operation. Writing only one half of the register will prevent the other half from being
written.
Soft reset has no effect on this register.
18.3.4 MISR High (MISRH) and MISR Low (MISRL)
The MISRH and MISRL together contain the 32-bit RAM signature calculated by the
MISC. These registers are read-only and should be read by the host when the MISF
bit in the MCR is set. Note that the naming of the D[31:0] bits represents little-endian
bit encoding.
Exiting TPU3 emulation mode results in the reset of both MISRH and MISRL
RAMBAR —
RAM Array Base Address Register
0x30 0004
MSB
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
LSB
15
A8
A9
A10
A11
A12
A13
A14
A15
A16
A17
A18
Reserved
RAMDS
RESET:
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
Table 18-3 RAMBAR Bit Descriptions
Bit(s)
Name
Description
0:10
A[8:18]
RAM array base address. These bits specify the 11 high-order bits (address lines ADDR[8:18]
in little-endian notation) of the 24-bit base address of the RAM array. This allows the array to be
placed on a 8-Kbyte boundary anywhere in the memory map. It is the users responsibility not to
overlap the RAM array memory map with other modules on the chip.
On the MPC555
/
MPC556 the value 0xFFA0 must be used.
11:14
—
Reserved. (Bits 11:12 represent A[19:20] in DPTRAM implementations that require them.
15
RAMDS
RAM disabled. RAMDS is a read-only status bit. The RAM array is disabled after a master reset
since the RAMBAR register may be incorrect. When the array is disabled, it will not respond to
any addresses on the IMB3. Access to the RAM control register block is not affected when the
array is disabled.
RAMDS is cleared by the DPTRAM module when a base address is written to the array address
field of RAMBAR.
RAMDS = 0: RAM enabled
RAMDS = 1: RAM disabled
MISRH —
Multiple Input Signature Register High
0x30 0006
MSB
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
LSB
15
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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