SH7280 Datasheet, PDF (409/1726 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine family

Section 9 Bus State Controller (BSC)
bus, the I bus, and the peripheral bus are synchronized with the Iφ, Bφ, and Pφ clock, respectively.
Figure 9.44 shows an example of the timing of write access to a peripheral bus when Iφ:Bφ:Pφ =
4:4:1. C bus whose are connected to CPU outputs data in synchronization with Iφ. A data transfer
from C bus to I bus requires a period of 2Iφ + Bφ when Iφ:Bφ = 1:1. The transfer from the I bus to
the peripheral bus, when Bφ:Pφ = 4:1, there are 4 clocks exist between Pφ × 1. Thus maximum the
period of 4 × Bφ is required corresponds to the rising edge of Pφ, which the timing of data output
to the peripheral bus from the I bus. When Iφ: Bφ = 4:2, transfer of data from the I bus to the
peripheral bus takes (3 + n) × Iφ (4 × Bφ is indicated in figure 9.44). The relation between the
timing of data output to the I bus and the rising edge of Pφ depends on the state of program
execution. In the case shown in the figure, where n = 0 and m = 3, the time required for access is 2
× Iφ + 4 × Bφ + 2 × Pφ.
Iφ
C bus
Bφ
I bus
Pφ
Peripheral bus
(2 + n) × Iφ (1 + m) × Bφ
2 × Pφ
Figure 9.44 Timing of Write Access to On-Chip Peripheral I/O Registers
When Iφ;Bφ:Pφ = 4:4:1
Figure 9.45 shows an example of timing of read access to the peripheral bus when Iφ:Bφ:Pφ =
4:2:1. Transfer from the C bus to the peripheral bus is performed in the same way as for write
access. In the case of reading, however, values output onto the peripheral bus must be transferred
to the CPU. Although transfers from the peripheral bus to the I bus and from the I bus to the C bus
are performed in synchronization with the rising edge of the respective bus clocks, a period of (2 +
l) × Iφ is actually required because Iφ ≥ Bφ≥ Pφ. In the case shown in the figure 9.45, where n = 1,
m = 1, and l = 1, the time required for access is 3 × Iφ + 2 × Bφ + 2 × Pφ + 3 × Iφ.
Rev. 1.00 Jun. 26, 2008 Page 379 of 1692
REJ09B0393-0100