ST10R272L - SYNCHRONOUS SERIAL PORT
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13.2.13 Visibility of accesses to the SSP
An access to the SSP can be made fully visible externally or not. This option is controlled by
the bit VISIBLE in register SYSCON. The grade of visibility depends on several conditions
described in the following.
13.2.14 Single chip mode
This description does not apply to the ST10R272L ROMless device, and only applies to
ST10 devices with internal Flash or ROM.
Single chip mode is entered during reset with pin EA tied to a logic high level. The chip will
start running in single chip mode without an external bus.
When bit VISIBLE in register SYSCON is cleared, SSP accesses will be completely hidden.
Although the SSP is connected to the XBUS, which is an internal implementation of the
external bus, it can be accessed in single chip mode without any restriction. No external bus
signal will be generated for an access to the SSP address range, because the XBUSACT bit
in register XBCON1 only controls accesses to the SSP via the XBUS, it does not control the
external bus (i.e. Port 0, Port 1, Port 4 and Port 6 can be used for general purpose I/O).
When bit VISIBLE in register SYSCON is set, then accesses to the SSP can be made visible
to the external world. To do so, one of the BUSCON registers has to enable a 16-bit
demultiplexed external bus (Port 0 and Port 1 cannot be used for general purpose I/O in this
case). All accesses to the SSP can be monitored externally, and read/write strobes are
generated. The visibility of the segment address depends on the number of segment
address lines selected for Port 4.
13.2.15 External bus mode
If an external bus is enabled through one or more of the BUSCON registers, PORT0,
PORT1, Port 4 and Port 6 (or parts of them) may be used to control the external bus.
When bit VISIBLE in register SYSCON is cleared, accesses to the SSP will be partly
reflected on the external bus. Due to severe timing constraints, it is not possible to hide SSP
accesses completely, when an external bus is enabled. SSP accesses will be reflected on
the external bus in the following manner:
•
The ALE signal will be generated in any case.
•
No read or write Signals will be generated.
•
The data of a read access cannot be seen.
•
The visibility of the segment address depends on the number of segment address lines
selected for Port 4.