MC68181 Datasheet, PDF (67/119 Pages) Freescale Semiconductor, Inc – Advance Information ROAMING FLEX chip SIGNAL PROCESSOR

Freescale Semiconductor, Inc.
MC68181
Host-to-Decoder Packet Descriptions
continues normally when the FLEX chip IC is “disabled”. The FLEX chip IC is only
disabled in the sense that the data can not be read from the FLEX chip IC, all other
operations continue to function. Disabled only implies that data cannot be read, all
other internal operations continue to function.
When the FLEX chip IC is reset, it is disabled and the internal checksum register is
initialized to the 24-bit part ID defined in the Part ID Packet. (See Part ID Packet on
page B-43.) Every time a packet other than the Checksum Packet and the special
packets 1C through 1F is sent to the decoder IC, the value sent in the 24 information
bits is exclusive-ORed with the internal checksum register, the result is stored back to
the checksum register, and the FLEX chip IC is disabled. If a Checksum Packet is sent
and the CV bits match the bits in the checksum register, the FLEX chip IC is enabled.
If a Checksum Packet is sent when the FLEX chip IC is already enabled, the packet is
ignored by the FLEX chip IC, in which case a null packet having the ID and data bits
set to 0 is suggested. If a packet other than the Checksum Packet is sent when the
FLEX chip IC is enabled, the decoder IC will be disabled until a Checksum Packet is
sent with the correct CV bits.
When the host reads a packet out of the FLEX chip IC but has no data to send, the
Checksum Packet should be sent so the FLEX chip IC will not be disabled. The data in
the Checksum Packet could be a null packet, 32-bit stream of all 0s, since a Checksum
Packet will not disable the FLEX chip IC. When the host re-configures the FLEX chip
IC, the FLEX chip IC will be disabled from sending any packets other than the Part ID
Packet until the FLEX chip IC is enabled with a Checksum Packet having the proper
data. The ID of the Checksum Packet is 0.
Table B-3 Checksum Packet Bit Assignments
Byte
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2
3
0
0
0
0
0
0
2
CV₂₃
CV₂₂
1
CV₁₅
CV₁₄
0
CV₇
CV₆
Note: CV = Checksum Value
CV₂₁
CV₁₃
CV₅
CV₂₀
CV₁₂
CV₄
CV₁₉
CV₁₁
CV₃
CV₁₈
CV₁₀
CV₂
Bit 1
0
CV₁₇
CV₉
CV₁
Bit 0
0
CV₁₆
CV₈
CV₀
MOTOROLA
MC68181 Technical Data Sheet
B-7
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