MC68306FC16B Freescale Semiconductor, MC68306FC16B Datasheet - Page 102

• Manufacturer Part Number: MC68306FC16B
• Description: IC MPU INTEGRATED 132-PQFP
• Manufacturer: Freescale Semiconductor

Specifications of MC68306FC16B

• Processor Type: M683xx 32-Bit
• Speed: 16MHz
• Voltage: 5V
• Mounting Type: Surface Mount
• Package / Case: 132-MQFP, 132-PQFP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Features: -

Figure 5-1 shows a method of expanding the number of chip selects in case more are
required for the application.
5.2.7 DRAM Control Registers
The DRAM address space decode mechanism is identical to the chip select mechanism.
Bank 0 has priority over bank 1, but all chip selects have priority over DRAM. The
MC68306 DRAM controller provides CAS-before-RAS refresh only. The refresh timer is a
programmable period counter that generates a refresh request every 16 to 4096 EXTAL
periods, programmable in 16 EXTAL period increments. Programming the refresh rate is
described in paragraph 5.2.7.1. When a refresh is pending, a refresh cycle is inserted at
the earliest availability of the RAS/CAS signals. Both banks and both bytes are refreshed
together.
The refresh timer is not affected by any reset, and refresh cycles will appear under reset.
The refresh timer is initialized by a write to the refresh rate register. When this register is
written, the first refresh occurs immediately, so the refresh rate should be programmed
after the DRAM configuration register DRDT bit. After power-up, the refresh rate register
value is random. If power consumption is critical, the refresh rate should be set as soon as
possible. In a system with soft-reset recovery, the hard/soft reset decision could take a
long time. A safe algorithm is to read the register first; if it contains the correct value, do
nothing. This will not disturb the timer, and the reset recovery can proceed at leisure.
Refresh stops only when the MC68306 is arbitrated off the bus. If the internal EC000 BG
signal is asserted while a refresh cycle is in progress, the external BG signal is delayed
until the refresh is complete. However, no refresh will occur during another master's
tenure of the bus if the BG or BGACK signals are recognized before a refresh cycle starts.
The task of DRAM refresh must be assumed by any other bus master. The refresh timer is
not suspended while the bus is arbitrated away, so a refresh cycle is likely when the
5-12
AMODE
MC68306
ADDR
CS0
CS1
CS2
CS3
CS4
CS5
CS6
CS7
}
Freescale Semiconductor, Inc.
1 MBYTE ADDRESS
Figure 5-1. Chip Select Expansion
For More Information On This Product,
SPACE EACH
MC68306 USER'S MANUAL
Go to: www.freescale.com
A15
A16
A19
A17
A18
2
4
6
1
3
5
A1
A0
A2
E1
E2
E3
74F138
Q1
Q2
Q3
Q4
Q5
Q6
Q0
Q7
32 KBYTE ADDRESS
EXCS0 ($080XXX)
EXCS1 ($088XXX)
EXCS2 ($090XXX)
EXCS3 ($098XXX)
EXCS4 ($0A0XXX)
EXCS5 ($0A8XXX)
EXCS7 ($0B8XXX)
EXCS6 ($0B0XXX)
SPACE EACH
MOTOROLA