Module Comparisons Third-Party Products Functional Information

DCF11 Processors


The DCF11-based processor is a microcomputer with a 16-bit address bus and a 16-bit data bus. It was used in the PDP-11/23 line of Q-bus computers, and the PDP-11/24 line of UNIBUS computers.

The CPU is made up of a chipset that consists of a dual chip, 40-pin ceramic carrier, containing the data and control functions. This carrier implements the the PDP-11 execution unit and instruction set. It also implements kernel and user modes, allowing more complex operating systems to be supported. Two more 40-pin sockets are provided for additional control units that are can be used to expand the instruction set.

The processor can address up to 64 KB of memory and reserves the top 8 KB of the address space for I/O devices. It is usually supplemented with the KTF11-AA memory management unit (MMU), which expands its address space from 16-bits to 22-bits, allowing up to 4 MB of memory to be accessed by the processor. The MMU also provides memory protection and includes the registers for the optional KEF11-AA floating point unit.

The table below contains a breakdown and comparison of the DCF11-based processors.

DCF11 Processors and Their Capabilities
Processor LSI-11/23 LSI-11/23+
Module Number M8186 M8189
Model Number KDF11-AA KDF11-AB KDF11-AC KDF11-BA KDF11-BB KDF11-BC KDF11-BD
Introduced 1979 1979 1979 1981 1981 1981 1981
Module Size Dual Dual Dual Quad Quad Quad Quad
Chipset F11 F11 F11 F11 F11 F11 F11
CIS Instructions optional1 no11 optional1 optional1 optional1 optional1 yes
EIS Instructions yes yes yes yes yes yes yes
FIS Instructions optional2 yes optional2 optional3 yes optional3 optional3
Memory Management yes yes optional4 yes yes optional4 yes
Performance (VUP) 0.12 0.12 0.12 0.18 0.18 0.18 0.18
Dhrystones12/sec 295/31613 295/31613 295/31613 295/31613 295/31613 295/31613 295/31613
Whetstones14 (KIPS) 22.9 22.9
Clock Period (ns)5 65-726 65-726 65-726 75 75 75 75
Q-bus Address Size 22-bits7 22-bits7 22-bits7 22-bits 22-bits 22-bits 22-bits
Q-bus Interrupts 4-level 4-level 4-level 4-level 4-level 4-level 4-level
RAM Capacity 4 MB8 4 MB8 4 MB9,8 4 MB 4 MB 4 MB9 4 MB
Onboard ROM no no no 4 KB10 4 KB10 4 KB10 4 KB10
Onboard LTC Register no no no yes yes yes yes
Onboard Serial Ports no no no 2 2 2 2
ODT Microcode yes yes yes yes yes yes yes
ODT Firmware no no no no no no no
Self-Test Diagostics no no no yes yes yes yes
Memory Refresh no no no yes yes yes yes
Termination 220 ohms 220 ohms 220 ohms 120 ohms 120 ohms 120 ohms 120 ohms
AC Bus Load 2 2 2 2 2 2 2
DC Bus Load 1 1 1 1 1 1 1
+5V Load 2.0 A 2.0 A 2.0 A 4.9 A 5.1 A 4.5 A 5.5 A
+12V Load 0.2 A 0.2 A 0.2 A 0.3 A 0.3 A 0.3 A 0.3 A

1 Requires the KEF11-B Commercial Instruction Set chip.
2 Requires the KTF11-AA MMU 21-15542-00 and CTL/DAT 57-00000-01, or later, plus the KEF11-AA floating point chip,
   or the M8188 FPF11-A Floating-Point Processor option module.
3 Requires the KEF11-AA floating point chip, or the M8188 FPF11-A Floating-Point Processor option module.
4 Requires the KTF11-AA MMU chip.
5 Clock frequency = 1 / Clock Period (e.g. 1 / 400 ns = 1 / 0.0000004 = 2,500,000 Hz, or 2.5 MHz)
6 Depending on the oscillator installed on the module.
7 Revision “A” modules support 18-bits, while Revision “C” and later modules support 22-bits.
8 Revision “A” modules are limited to 256 KB.
9 Requires the KTF11-AA MMU chip. Modules without the MMU are limited to 64 KB.
10 The KDF11-B is equipped with two 24-pin sockets, accepting 2 KB, 4 KB, or 8 KB ROMs.
11 The KDF11-A does not have enough sockets to simultaneously support the FIS and CIS chipsets.
12 Average performance measured using the C version of Dhrystone v2.1.
13 Running under 2.9BSD in single user mode. The first number is without register declarations, the second is with register declarations.
14 Average performance measured using the C version of Whetstone v2.1.

M8189 Module Numbers

When the MicroPDP-11/23 came along, the M8189 module numbers changed to reflect the installed boot ROMs, instead of the actual processor configuration. It is assumed the actual hardware configuration is the KDF11-BA configuration, with MMU, no FIS, and no CIS. The new module numbers are as follows:

M8189 EPROMs

The M8189 is equipped with two 24-pin sockets, for holding boot firmware, and the size of these sockets limits the parts that can be used. The following is a short list of EPROMs that are compatible with the M8189. The firmware part numbers listed above ending in E2 will fit in a 2K EPROM. The part numbers ending in E4 require an 8K EPROM.


Either processor would be desirable to own, but the M8189 provides more value. An M8186 would require additional modules with serial ports, boot ROMs and potentially an LTC register to provide a complete system. This could be accomplished by pairing it with a multifunction board, but it would still take up as much or more space as the M8189. In small form factor systems, with an H9281 backplane, the M8186 would be the only choice.

The most important thing to watch out for with the M8186 is the etch revision of the circuit board. The earlier etch Revision A board is only wired for 18 bits. Etch Revision C and later circuit boards are wired for 22 bits. Revision A boards are difficult to find, but it still helps to know this. If your system is going to have less than 256 KB of memory, then any board revision will work fine. DEC MicroNote 17 discusses, in great detail, the various KDF11-A revisions.

The photo below shows an M8186 circuit board with the etch revision (C) circled in red. This means the module supports 22-bit addresses. The seven digit number preceding the revision is DEC's part number for the raw printed circuit board itself.

M8186 Processor PCB Identification

To access more than 64 KB of memory, the processor needs a memory management unit. Most F11 modules were shipped with these, but you can still find modules with no MMU installed.


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