ST10 STMICROELECTRONICS [STMicroelectronics], ST10 Datasheet - Page 13

• Manufacturer Part Number: ST10
• Description: 16-BIT MCU WITH 32K BYTE ROM
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

VI - EXTERNAL BUS CONTROLLER
All of the external memory accesses are per-
formed by the on-chip external bus controller. The
EBC can be programmed to single chip mode
when no external memory is required, or to one of
four different external memory access modes:
– 16-/18-/20-/24-bit addresses and 16-bit data,
– 16-/18-/20-/24-bit addresses and 16-bit data,
– 16-/18-/20-/24-bit addresses and 8-bit data,
– 16-/18-/20-/24-bit addresses and 8-bit data, de-
In 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.
Timing characteristics of the external bus inter-
face (memory cycle time, memory tri-state time,
length of ALE and read/write delay) are program-
mable giving the choice of a wide range of memo-
ries and external peripherals. Up to 4 independent
address windows may be defined (using register
pairs ADDRSELx / BUSCONx) to access different
resources and 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 con-
trolled by BUSCON0. Up to 5 external CS signals
(4 windows plus default) can be generated in
order to save external glue logic. Access to very
slow memories is supported by a ‘Ready’ function.
demultiplexed.
multiplexed.
multiplexed.
multiplexed.
A HOLD/HLDA protocol is available for bus arbi-
tration which shares external resources with other
bus masters. The bus arbitration is enabled by
setting bit HLDEN in register SYSCON. After set-
ting 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 directly connects the slave
controller to another master controller without
glue logic.
For applications which require less external mem-
ory space, the address space can be restricted to
1M Byte, 256K Byte or to 64K Byte. Port 4 outputs
all 8 address lines if an address space of
16M Byte is used, otherwise four, two or no
address lines.
Chip select timing can be made programmable.
By default (after reset), the CSx lines change half
a CPU clock cycle after the rising edge of ALE.
With the CSCFG bit set in the SYSCON register
the CSx lines change with the rising edge of ALE.
The active level of the READY pin can be set by
bit RDYPOL in the BUSCONx registers. When the
READY function is enabled for a specific address
window, each bus cycle within the window must
be terminated with the active level defined by bit
RDYPOL in the associated BUSCON register.
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