Host Access Modes and Timings
MSC8113 Reference Manual, Rev. 0
Freescale Semiconductor
14-17
14.3.3.4 Asynchronous Read Using Single Strobe Mode
Figure 14-10 shows an asynchronous read access using Single Strobe mode. The DSI samples
the host address bus (
HA[11–29])
and the
HCID
on the first falling edge of the Host Data Byte Strobe
signals (
HDBS
) on which the
HCS
is asserted with
HRW
driven high. If
HCID[0–3]
match the
CHIPID value, the DSI is accessed. When the DCR[RPE] bit is set, read access to the memory
space (not to the register space) initiates data prefetching from consecutive addresses in the
internal memory space. Assertion of
HTA
indicates that data is valid, and the host can sample the
host data bus (
HD
) and terminate the access by deasserting
HDBS
. If the data for this access is
already in the read buffer due to the prefetch mechanism, the assertion time of
HTA
is improved.
The DCR[HTAAD] and DCR[HTADT] bits determine which of the following actions the DSI
takes at the rising edge of
HRDS
:
Stop driving
HTA
. DCR[HTAAD] = 0 and DCR[HTADT] = 00. This mode requires a
pull-down resistor on
HTA
.
Drive
HTA
high. DCR[HTAAD] = 1 and DCR[HTADT]
≠
00. The DCR[HTADT] value
indicates the amount of time to drive
HTA
. This mode requires a pull-up resistor on
HTA
.
In either case, the host can start a back-to-back access without deasserting
HCS
between accesses.
When DCR[HTAAD] and DCR[HTADT] are both cleared, the host must ignore the
HTA
value
from the start of the access until the DSI drives it to its correct value. The required delay period is
defined in the AC characteristics section of the MSC8113 Technical Data sheet. If
DCR[HTAAD] is set and DCR[HTADT] does not equal 00 and the next access is not to the same
MSC8113, then to prevent contention on the
HTA
signal, the host must wait until the previous DSI
stops driving the
HTA
signal before it accesses the next device. When the DCR[HTAAD] bit is set
and the next access is to the same MSC8113, the host must not start consecutive access before the
previous access deasserts
HTA
.
Figure 14-10. Asynchronous Read Using Single Strobe Mode
don’t care
HCS
HTA (output)
HRW
HD[0–63] (output)
HCID[0–3]
HA[11–29]
HDST[0–1]
valid value
valid value
valid value
valid value
HTAAD = 1 and HTADT = 01,10,11
HTAAD = 0 and HTADT = 00
don’t care
don’t care
don’t care
don’t care
don’t care
don’t care
don’t care
HDBS[0–7]
don’t care
don’t
care
don’t care
don’t care
valid value
valid value
valid value
Note: The signal timing shown for HDBS[0–7] is for signals that are asserted. Unused signals remain high (deasserted).
Содержание MSC8113
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Страница 304: ...MSC8113 Reference Manual Rev 0 10 4 Freescale Semiconductor MQBus and M2 Memory ...
Страница 308: ...MSC8113 Reference Manual Rev 0 11 4 Freescale Semiconductor SQBus ...
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Страница 622: ...MSC8113 Reference Manual Rev 0 19 8 Freescale Semiconductor Internal Peripheral Bus IPBus ...
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