Motorola MPC8260 User Manual

MOTOROLA

Chapter 27.  Multi-Channel Controllers (MCCs)  

27-3

0x00

Word

Multi-channel controller base pointer. User-initialized parameter points to the starting 
address of a 512-Kbyte BD segment in external memory.

0x04

Hword Multi-channel controller state, used by the CP for global state deÞnition (reserved for 

the user)

0x06

Hword Maximum receive buffer length (user-initialized). DeÞnes the maximum number of 

bytes written to a receive buffer before moving to the next buffer for this channel. 
This value must be a multiple of 8.

0x08

Hword Global receive frame threshold. Used to reduce interrupt overhead that can occur 

when many short HDLC frames arrive that each cause an RXF interrupt. Setting all 
bits enables every interrupt event. Setting a GRFTHR value can limit the frequency 
of RXF interrupts. Note that an RXF event is written to the interrupt queue on each 
received frame but GINT is set only when the number of RXF events (by all 
channels) reaches the GRFTHR value. This parameter does not need to be reset 
after an interrupt. 

0x0A

Hword Global receive frame count. A decrementor counter used to implement the GRFTHR 

feature. It should be initialized to the GRFTHR value. Setting all bits enables every 
interrupt event. The CP writes an entry in a circular interrupt table and decrements 
GRFCNT each time a frame is received. When GRFCNT underßows the CP 
generates an interrupt and copy GRFTHR to GRFCNT. This parameter does not 
need to be reset after an interrupt. 

Channel j TxBD 

Table

Channel 0 Parameter

Channel 1 Parameter

Channel j Extra

RBASE

TBASE

Global MCC 

MCCBASE

DPR

Buffer Descriptor 

+

+

Channel j RxBD 

Table

External Memory

512 Kbytes

x8

x8

DPR_base

Table Base Address

Parameter

Parameters