Toshiba H1 Series - Manual (Page 111)

TMP92CZ26A
92CZ26A-108
HDMATR Register
7 6 5 4 3 2 1 0
bit Symbol DMATE DMATR6 DMATR5 DMATR4 DMATR3 DMATR2 DMATR1 DMATR0
Read/Write R/W
After reset 0 0 0 0 0 0 0 0
Function
Timer
operation
0: Disable
1: Enable
Maximum bus occupancy time setting
The value to be set in <DMATR6:0> should be obtained by
“maximum bus occupancy time / (256/fSYS)”.
“00H” cannot be set.
Note: Read-modify-write instructions can be used on this register.
By writing “87H” to the HDMATR register, the maximum HDMA time is set to 29.9 [ μs]
(256 Ч 7 Ч (1 / f
SYS
)). Since HDMA start interval [period:s] = 83.33 [ms] is longer than
LHSYNC [period:s] = 54.95 [ μs], it is assumed that HDMA transfer occurs once during
LHSYNC [period:s].
Since SDRAM is auto-refreshed once or less in 5.47 [
μs]:
t
STOP
(ARDMA) = 2 / f
SYS
[Hz] = 33.33 [ns]
The time LDMA, ARDMA, and HDMA all occupy the bus is defined as:
t
STOP
(LDMA ARDMA HDMA)
Based on the above, the CPU bus stop rate is calculated as follows:
CPU bus stop rate = t
STOP
(LDMA ARDMA HDMA) [s] / LHSYNC [period:s]
= (5.47 [μs] + 33.33 [ns]+29.9 [μs]) / 54.95 [μs] = 64.42 [%]
Note: To be precise, the bus assert time and RAM access time are added each time the HDMA transfer time is
forcefully terminated at 29.9 [
μs].
HDMATR
(097FH)