Communications Processor
MPC885 PowerQUICC Family Reference Manual, Rev. 2
Freescale Semiconductor
18-11
Figure 18-6. Dual-Port RAM Block Diagram
The dual-port RAM consists of 7 Kbytes of system RAM (see
Section 18.7.1, “System RAM and
Microcode Packages”
) and 1 Kbyte of parameter RAM (see
Section 18.7.3, “Parameter RAM”
) and is
used for the following:
•
Storing parameters associated with the USB, SCCs, SMCs, SPI, I
2
C, and IDMAs (in parameter
RAM only)
•
Storing the BDs (in any unused dual-port RAM area)
•
Storing buffers (in any unused dual-port RAM area or external memory)
•
Storing Freescale-supplied microcode for the CP (in system RAM only)
•
Scratch pad area for user software (in any unused dual-port RAM area)
The dual-port RAM can be accessed either by the CP or by one of two internal U-bus masters—the
MPC8xx core or an SDMA channel. The core and the SDMA channels access the dual-port RAM in two
clocks, while the CP takes only one clock. For simultaneous accesses with at least one write operation, the
CP is delayed by one clock.
When the core or SDMA channel access the dual-port RAM, the data and address are passed through the
U-bus. The CP can fetch data from the entire dual-port RAM and microcode instructions from portions of
the system RAM.
The controller and sub-block parameters of the parameter RAM and the optional microcode packages in
system RAM use fixed addresses. The buffer descriptors, buffers, and scratch pad area, however, can be
located in any unused dual-port RAM area. See
Figure 18-7
.
Address
Selectors
Data
Selectors
U-Bus Addr
CP Microcode Instr Addr
CP Data Addr
U-Bus Addr
CP Data Addr
CP Microcode Instr
U-Bus Data
CP Data
Shaded area is system RAM. Note that in this figure, the area is not contiguous memory. For an accurate
representation of the physical implementation, see
Figure 18-7
.
Address
Selectors
Data
Selectors
1,024 Bytes
BD/Buffers/Microcode
1,024 Bytes
BD/Buffers/Microcode
512 Bytes
BD/Buffers/Microcode
1,024 Bytes
BD/Buffers/Microcode
512 Bytes
BD/Buffers/Microcode
2,048 Bytes
BD/Buffers
1,024 Bytes
Parameter RAM
Dual-Port
1,024 Bytes
BD/Buffers/Microcode
Summary of Contents for PowerQUICC MPC870
Page 98: ...MPC885 PowerQUICC Family Reference Manual Rev 2 I 4 Freescale Semiconductor ...
Page 118: ...MPC885 Overview MPC885 PowerQUICC Family Reference Manual Rev 2 1 20 Freescale Semiconductor ...
Page 158: ...The MPC8xx Core MPC885 PowerQUICC Family Reference Manual Rev 2 3 18 Freescale Semiconductor ...
Page 288: ...MPC885 PowerQUICC Family Reference Manual Rev 2 III 4 Freescale Semiconductor ...
Page 554: ...MPC885 PowerQUICC Family Reference Manual Rev 2 V 6 Freescale Semiconductor ...
Page 1090: ...UTOPIA Interface MPC885 PowerQUICC Family Reference Manual Rev 2 43 8 Freescale Semiconductor ...
Page 1312: ...Byte Ordering MPC885 PowerQUICC Family Reference Manual Rev 2 A 8 Freescale Semiconductor ...
Page 1336: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 16 Freescale Semiconductor ...
Page 1358: ...MPC885 PowerQUICC Family Reference Manual Rev 2 D 38 Freescale Semiconductor ...
Page 1370: ...MPC880 MPC885 PowerQUICC Family Reference Manual Rev 2 E 4 Freescale Semiconductor ...
Page 1386: ...Revision History MPC885 PowerQUICC Family Reference Manual Rev 2 I 2 Freescale Semiconductor ...