3.0 Expansion Bus (EBUS)
CN8478/CN8474A/CN8472A/CN8471A
3.1 Operation
Multichannel Synchronous Communications Controller (MUSYCC™)
For Motorola-style interfaces, the arbitration protocol is as follows (refer to
Figure 7-14, EBUS Write/Read Transactions, Motorola-Style):
1. MUSYCC three-states EAD[31:0], EBE*[3:0]. R/WR*, DS*, and AS*.
2. MUSYCC requires EBUS access and asserts BR*.
3. MUSYCC checks for BG* assertion by bus arbiter.
4. If BG* is deasserted, MUSYCC waits for the BG* signal to become
asserted before continuing the EBUS operation.
5. If BG* is asserted, MUSYCC continues with the EBUS access as it has
control of the EBUS.
6. If BGACK* is deasserted, MUSYCC assumes control of the EBUS by
asserting BGACK*.
7. MUSYCC drives EAD[31:0], EBE*[3:0], R/WR*, DS*, AS*.
8. Shortly after the EBUS cycle is started, MUSYCC deasserts BR*.
9. Bus arbiter deasserts BG* shortly thereafter.
10. MUSYCC completes EBUS cycle.
11. MUSYCC deasserts BGACK*.
12. MUSYCC three-states EAD[31:0], EBE*[3:0]. R/WR*, DS*, and AS*.
3.1.11 Connection
Using the EBUS address lines, EAD[17:0], and the byte enable lines, EBE[3:0]*,
the EBUS can be connected in either a multiplexed or non-multiplexed address
and data mode.
Figures 3-4 and 3-5 illustrate two examples of non-multiplexed address and
data modes. These figures illustrate four separate byte-wide framer devices
connected to the EBUS with each byte enable line used as the chip select for
separate devices. This allows a full dword data transfer over the EBUS.
Figure 3-4. EBUS Connection, Non-multiplexed Address/Data, 8 Framers, No MPU
EAD[31:24]
EAD[23:16]
EAD[31:0]
EAD[15:8]
EAD[7:0]
EAD[8:0]
Data Addr
CN8370
CS*
Data Addr
CN8370
CS*
Data Addr
CN8370
CS*
Data Addr
CN8370
CS*
EINT*
AS*, R/WR*, DS*,
ECLK Control Lines
Device 0,4
Device 1,5
Device 2,6
Device 3,7
EAD9
EBE[0]*
EBE[1]*
dev 0,4
Chip
Select
Logic
EBE[3:0]*
EBE[2]*
EBE[3]*
8478_010
3-8
Conexant
100660E
CONEXANT [ CONEXANT SYSTEMS, INC ]
