Motorola MPC823e

Communication Processor Module
MOTOROLA MPC823e REFERENCE MANUAL 16-463
I
2
C
COMMUNICATION
16
PROCESSOR MODULE
16.13.4 I
2
C Parameter RAM Memory Map
The I
2
C controller parameter RAM area begins at the I
2
C base address, which is used for
the general I
2
C parameters. It is similar to the SCCx general-purpose parameter RAM. You
must initialize certain parameter RAM values before the serial peripheral interface is
enabled. The communication processor module initializes the other values. Once initialized,
the parameter RAM values do not usually need to be accessed by your software. They must
only be modified when there is no serial peripheral interface activity.
• RBASE and TBASE—The dual-port RAM starts receiving and transmitting data for the
I
2
C buffer descriptors in the RBASE and TBASE entries. They provide a great deal of
flexibility for partitioning buffer descriptors for an I
2
C controller. By selecting RBASE and
TBASE for the I
2
C controller and by setting the W bit in the last buffer descriptor in each
buffer descriptor list, you can select the number of buffer descriptors to allocate for the
transmit and receive side of the I
2
C controller. However, you must initialize these entries
before enabling the corresponding channel. Furthermore, you must not configure the
buffer descriptor tables of the I
2
C controller to overlap because erratic operation will
occur. RBASE and TBASE must contain a value that is divisible by eight.
Table 16-40. I
2
C Controller Parameter RAM Memory Map
ADDRESS NAME WIDTH DESCRIPTION
I
2
C Base + 00
RBASE Half-word RX Buffer Descriptor Base Address
I
2
C Base+ 02
TBASE Half-word TX Buffer Descriptor Base Address
I
2
C Base+ 04
RFCR Byte RX Function Code
I
2
C Base+ 05
TFCR Byte TX Function Code
I
2
C Base+ 06
MRBLR Half-word Maximum Receive Buffer Length
I
2
C Base+ 08
RSTATE Word RX Internal State
I
2
C Base+ 0C
RPTR Word RX Internal Data Pointer
I
2
C Base+ 10
RBPTR Half-word RX Buffer Descriptor Pointer
I
2
C Base+ 12
RCNT Half-word RX Internal Byte Count
I
2
C Base+ 14
RTMP Word RX Temp
I
2
C Base+ 18
TSTATE Word TX Internal State
I
2
C Base+ 1C
TPTR Word TX Internal Data Pointer
I
2
C Base+ 20
TBPTR Half-word TX Buffer Descriptor Pointer
I
2
C Base+ 22
TCNT Half-word TX Internal Byte Count
I
2
C Base+ 24
TTMP Word TX Temp
NOTE: You are only responsible for initializing the items in bold. I
2
C Base = (IMMR & 0xFFFF0000) + 0x3C80.