Datasheet

www.ti.com N2HET Functional Description
23.2.4.2 64-bit Read Access
The consecutive read of a control field CF(n) and a data field DF(n) of the same instruction (n) performed
by the same master (for example, CPU, DMA, or any other master) is always done as a simultaneous 64-
bit read access. This means that at the same time CF(n) is read, DF(n) is loaded in a shadow register. So
the second access will read DF(n) from the shadow register instead of the N2HET RAM.
In general a 64-bit read access of one master could be interrupted by a 64-bit read access of another
master. A total of three shadow registers are available. Therefore up to three masters can perform 64-bit
reads in an interleaved manner (Master1 CF, Master2 CF, Master3 CF, Master1 DF, Master2 DF, Master3
DF).
If all three shadow registers are activated and a 4th master performs a CF or DF read it will result in an
address error and the RAM access will not happen. Other access types by a fourth master (reads from the
PF field or writes to any of the fields) will occur because these access types do not require an available
shadow register resource to complete.
23.2.4.3 Automatic Read Clear Feature
The N2HET provides a feature allowing to automatically clear the data field immediately after the data field
is read by the external host CPU (or DMA). This feature is implemented via the control bit, which is
located in the control field (bit C26). This is a static bit that can be used by any instruction, and specified in
the N2HET program by adding the option (control = ON) to the N2HET instruction. The automatic read
clear feature works for both 32 and 64 bit reads that follow the sequence described in Section 23.2.4.2.
When the host CPU reads the data field of that instruction, the current data value is returned to the host
CPU but the field is cleared automatically as a side effect of the read. In case the master reads data from
an instruction currently executing, any new capture result is stored and this takes priority over the
automatic read clear feature, so that the new capture result is not lost.
As an example of where the automatic read clear feature is useful, consider the PCNT instruction. If this
instruction is configured for automatic read clear, then when the host CPU reads the PCNT data field it will
be cleared automatically. The host CPU can then poll the PCNT data field again, and as long as the field
returns a value of zero the host CPU program knows a new capture event has not occurred. If the data
field were not cleared, it would be impossible for the host CPU to determine whether the data field holds
data from the previous capture event, or if it happens to be data from a new capture event with the same
value.
23.2.4.4 Emulation Mode
Emulation mode, used by the software debugger, is specified in the global configuration register. When
the host CPU debugger hits a breakpoint, the CPU sends a suspend signal to the modules. Two modes of
operation are provided: suspend and ignore suspend.
• Suspend
When a suspend is issued, the timer operation stops at the end of the current timer instruction. However,
the CPU accesses to the timer RAM or control registers are freely executed.
• Ignore suspend
The timer RAM ignores the suspend signal and operates real time as normal.
23.2.4.5 Power-Down
After setting the turn-off bit in the Global Configuration Register (HETGCR), it is required to delay until the
end of the timer program loop before putting the N2HET in power-down mode. This can be done by
waiting until the N2HET Current Address (HETADDR) becomes zero, before disabling the N2HET clock
source in the device’s Global Clock Module (GCM).
23.2.5 I/O Control
The N2HET has up to 32 pins. Refer to device specific data sheets for information concerning the number
of N2HETIO available. All of the N2HET pins available are programmable as either inputs or outputs.
945
SPNU562–May 2014 High-End Timer (N2HET) Module
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