Rainbow Electronics DS3134 - Manual (Page 165)

DS3134
165 of 203
Configuration Mode Figure 10.1C
PCI Bridge Mode
In the PCI Bridge Mode, data from the PCI bus can be transferred to the Local Bus. In this mode, the
Local Bus acts as a "master" and can create all the needed signals to control the bus. In the PCI Bridge
Mode, the user must configure the Local Bus Bridge Mode Control Register (LBBMC) which is described
in Section 10.2.
With 20 address lines, the Local Bus can address a 1M byte address space. The Host on the PCI bus will
determine where to map this 1M byte address space within the 32-bit address space of the PCI bus by
configuring the Base Address in the PCI Configuration Registers (see Section 9).
Bridge Mode 8 & 16 Bit Access
During a bus access by the Host, the Local Bus can determine how to map the four possible byte positions
from/to the PCI bus to/from the Local Bus data bus (LD) pins by examining the PCBE* signals and the
Local Bus Width (LBW) control bit which resides in the Local Bus Bridge Mode Control (LBBMC)
register. If the Local Bus is to be used as an 8-bit bus (LBW = 1), then the Host must only assert one of
the PCBE* signals. The PCI data will be mapped to/from the LD[7:0] signal lines, the LD[15:0] signal
lines remain inactive. The Local Bus Block will drive the A0 and A1 address lines according to the
assertion of the PCBE* signals by the Host. See Table 10.1B for details. If the Host asserts more than
one of the PCBE* signals when the Local Bus is configured as an 8-bit bus, then the Local Bus will reject
the access and the PCI Block will return a Target Abort to the Host. See Section 9 for details on a Target
Abort.
T1 / E1
Framer or
Transceiver
Local Bus
DS3134 Chateau
Host
Processor
and Main
Memory
PCI /
Custom
Bus
lb_cnfgc
CPU Confgures and
Monitors DS3134
Local RAM &
ROM
No
Access
Allowed
Only Used to
Transfer HDLC
Data
T1 / E1
Framer or
Transceiver
T1 / E1
Framer or
Transceiver
T1 / E1
Framer or
Transceiver