SAB-C167CR-LM

Manufacturer Part NumberSAB-C167CR-LM
Description16-bit microcontroller with 2x2 KByte RAM
ManufacturerInfineon Technologies AG
SAB-C167CR-LM datasheet
 
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Page 19/74:

External Bus Controller

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C167CR
C167SR
External Bus Controller
All of the external memory accesses are performed by a particular on-chip External Bus
Controller (EBC). It can be programmed either to Single Chip Mode when no external
memory is required, or to one of four different external memory access modes, which are
as follows:
– 16-/18-/20-/24-bit Addresses, 16-bit Data, Demultiplexed
– 16-/18-/20-/24-bit Addresses, 16-bit Data, Multiplexed
– 16-/18-/20-/24-bit Addresses, 8-bit Data, Multiplexed
– 16-/18-/20-/24-bit Addresses, 8-bit Data, Demultiplexed
In the demultiplexed bus modes, addresses are output on PORT1 and data is input/
output on PORT0 or P0L, respectively. In the multiplexed bus modes both addresses
and data use PORT0 for input/output.
Important timing characteristics of the external bus interface (Memory Cycle Time,
Memory Tri-State Time, Length of ALE and Read Write Delay) have been made
programmable to allow the user the adaption of a wide range of different types of
memories and external peripherals.
In addition, up to 4 independent address windows may be defined (via register pairs
ADDRSELx / BUSCONx) which control the access to different resources with different
bus characteristics. These address windows are arranged hierarchically where
BUSCON4 overrides BUSCON3 and BUSCON2 overrides BUSCON1. All accesses to
locations not covered by these 4 address windows are controlled by BUSCON0.
Up to 5 external CS signals (4 windows plus default) can be generated in order to save
external glue logic. The C167CR offers the possibility to switch the CS outputs to an
unlatched mode. In this mode the internal filter logic is switched off and the CS signals
are directly generated from the address. The unlatched CS mode is enabled by setting
CSCFG (SYSCON.6).
Access to very slow memories or memories with varying access times is supported via
a particular ‘Ready’ function.
A HOLD/HLDA protocol is available for bus arbitration and allows to share external
resources with other bus masters. The bus arbitration is enabled by setting bit HLDEN
in register PSW. After setting HLDEN once, pins P6.7 … P6.5 (BREQ, HLDA, HOLD)
are automatically controlled by the EBC. In Master Mode (default after reset) the HLDA
pin is an output. By setting bit DP6.7 to ‘1’ the Slave Mode is selected where pin HLDA
is switched to input. This allows to directly connect the slave controller to another master
controller without glue logic.
For applications which require less than 16 MBytes of external memory space, this
address space can be restricted to 1 MByte, 256 KByte, or to 64 KByte. In this case
Port 4 outputs four, two, or no address lines at all. It outputs all 8 address lines, if an
address space of 16 MBytes is used.
Data Sheet
15
V3.2, 2001-07