Motorola MPC8260 - Manual (Page 740)

27-10 MPC8260 PowerQUICC II UserÕs Manual MOTOROLA
Part IV. Communications Processor Module
To enable an interrupt, set the corresponding bit. If a bit is cleared, no interrupt request is
generated and no new entry is written in the circular interrupt table. The user must initialize
INTMSK prior to operation. Reserved bits are cleared.
27.6.3 Channel Mode Register (CHAMR)
The channel mode register (CHAMR) is a user-initialized register, shown in Figure 27-8.
This is a generalized representation of CHAMR. Section 27.7.1, ÒChannel Mode Register
(CHAMR)ÑTransparent Mode,Ó describes the CHAMR for transparent mode.
CHAMR Þelds are described in Table 27-5.
Bits 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Interrupt Entry Ñ UN TXB Ñ NID IDL MRF RXF BSY RXB
INTMSK Ñ Mask Bits Ñ Mask Bits
Figure 27-7. INTMSK Mask Bits
Bits 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Field MODE POL 1 IDLM Ñ CRC Ñ TS RQN NOF
Reset Ñ
R/W R/W
Offset 0x1A
Figure 27-8. Channel Mode Register (CHAMR)
Table 27-5. CHAMR Field Descriptions
Bits Name Description
0 MODE This mode bit determines whether the HDLC or transparent mode is used. It also determines how
other CHAMR bits are interpreted.
0 Transparent mode. See Section 27.7.1, ÒChannel Mode Register (CHAMR)ÑTransparent Mode.Ó
1 HDLC mode
1 POL Enable polling. POL enables the transmitter to poll the TxBDs.
0 Polling is disabled (The CPM does not access the external bus to check the R bit in the TxBD).
1 Polling is enabled.
POL can be used to optimize the use of the external bus. Software should always set POL at the
beginning of a transmit sequence of one or more frames. The CP clears POL when no more buffers
are ready in the transmit queue, i.e. when it Þnds a BD with R = 0 (for example, at the end of a frame
or at the end of a multi-frame transmission). To minimize useless transactions on the external bus,
software should always prepare the new BD, or multiple BDs, and set BD[R] before enabling polling.
2 1 Must be set.