
IBM3206K0424
IBM Processor for Network Resources
Preliminary
The DRAM Controllers (COMET/PAKIT)
Page 184 of 676
pnr25.chapt04.01
August 14, 2000
Memory Controlling Entities
Entity 5: The DRAM Controllers (COMET/PAKIT)
This section describes the function of the COMET/PAKIT entities. COMET is the memory controller for Con-
trol Memory, and PAKIT is the memory controller for Packet Memory. 
Each controller can support the following types of memory: 
 Synchronous DRAMs running at 133MHz (7.5 ns cycle time) with a CAS latency of two or three and a 
burst length of one or two. Memory sizes of 4MB, 8MB, 16MB, and 32MB are supported. Please note that 
the cycle time of the SDRAM clock is a constant on the IBM3206K0424. Any SDRAM part selected must 
be capable of running at 133MHz or faster at CAS latency 2 or 3. 
 Synchronous SRAM running at 133MHz (7.5 ns cycle time) with a read latency of two and a write latency 
of zero or two. Memory sizes of 1MB, 2MB, 4MB, and 8MB are supported. 
Note:  
For any memory configuration, modules must be selected such that the loading on any memory net 
(including card wiring) does not exceed 120pF. 
The number of column address lines is programmable, allowing both DRAMs with symmetric address (same 
number of row and column address lines) and asymmetric address (typically having more row than column 
address lines). 
If using SDRAM, the memory may be operated as having one or two arrays. The arrays are differentiated by 
their chip selects. If the memory is configured to have two arrays, the memory's address range is split equally 
between the two arrays. 
Memory checking can be enabled/disabled, and the method of checking selected can be either ECC or parity. 
IF ECC is selected, seven data bits are used for ECC over the 32 data bits. If parity is selected, four data bits 
are used to provide parity over the 32 data bits. 
COMET/PAKIT are designed so that memory contents are preserved over a reset. If the IBM3206K0424 is 
reset while a memory write cycle is in progress, the cycle is completed in an orderly fashion to ensure that 
valid ECC/parity is written. Memory timings are not violated when reset goes active. Refresh is maintained 
during the reset.