| CDC 1700 Simulator | |
| ================== | |
| 1. Overview. | |
| The CDC 1700 was a 16-bit mini-computer produced by the Control Data | |
| Corporation with deliveries beginning in May 1966. | |
| 2. Hardware | |
| This simulator provides support for a subset of available peripherals, | |
| mostly from the early period of its release: | |
| device name Hardware | |
| CPU 1714 CPU with 4KW, 8KW, 16KW or 32KW of memory | |
| 1705 Multi-Level Interrupt and Direct Storage Access | |
| Bus | |
| Optional extensions: | |
| 64KW of memory with indirect addressing changes | |
| Character addressing option | |
| RTC 10336-1 Real-time clock | |
| Default tick interval is 10mSec, can be changed with | |
| "set rtc rate=<rate>" command, where <rate> is | |
| {1usec|10usec|100usec|1msec|10msec|100msec|1second}. | |
| [ Equipment address: 0xD] | |
| DCA Data channels providing DMA access to non-DMA | |
| DCB peripherals. The configuration is currently fixed | |
| DCC with DCA providing access to the magtape controller | |
| if it is configured as a 1732-A. | |
| TTI 1711-A Half-duplex console terminal. | |
| TTO [Equipment address: 0x1, Station address: 1] | |
| PTR 1721-A Paper tape reader | |
| [Equipment address: 0x1, Station address: 2] | |
| PTP 1723-A Paper tape punch | |
| [Equipment address: 0x1, Station address: 4] | |
| MT 1732-A or 1732-3 Magtape controller, 3 9-track drives | |
| (MT0 - MT2) and 1 7-track drive (MT3). The type of | |
| the controller may be changed using the command | |
| "set mt type={1732-A|1732-3}". The 1732-A controller | |
| supports 200, 556 and 800 BPI on the 9 track drives | |
| and allows DMA access via a 1706 Buffered Data | |
| Channel (device DCA). The 1733-3 controller supports | |
| 556, 800 and 1600 BPI on the 9 track drives and | |
| includes DSA (DMA) access built into the controller. | |
| Access via a 1706 Buffered Data Channel is not | |
| available. | |
| [Equipment address: 0x7] | |
| LP 1740 or 1742-30 Line printer (Upper case only). The | |
| type of the printer may be changed with the command | |
| "set lp type={1740|1742}; The 1742-30 is compatible | |
| with the 1742-120 but not allow the print train | |
| configuration to be loaded by software. | |
| [Equipment address: 0x4] | |
| DP 1738-B Disk pack controller. Supports up to 2 | |
| disk pack drives: | |
| 853 drive - 3072000 bytes | |
| 854 drive - 6236160 bytes | |
| [Equipment address: 0x3] | |
| CDD 1733-2 Cartridge disk pack controller. Supports up to | |
| 4 cartridge disk drives. Each drive supports a fixed | |
| and a removeable disk: | |
| 856-2 drive - 2260608 bytes | |
| 856-4 drive - 4543488 bytes | |
| [Equipment address: 0x3] | |
| DRM 1752 Drum memory controller with 64 - 1024 tracks of | |
| drum memory (each track is 3072 words). | |
| [Equipment address: 0x2] | |
| Notes: | |
| DP and CDD use the same equipment address so only 1 of them may be | |
| enabled (default is for CDD to be enabled). | |
| Both controllers use checkwords (CRC) for validating the consistency | |
| of the data stored on disk. The DP controller exports a single status | |
| bit indicating whether the checkword is valid or not (the simulator | |
| always sets this to valid). The CDD controller also exports a single | |
| status bit which is handled in the same way as the DP controller. | |
| It also makes the actual checkword value available. The simulator | |
| always returns a checkword value of 0 so any attempt to verify the | |
| checkword (such as some diagnostics) will fail. | |
| 3. Loading Software | |
| The simulator implements 2 mechanisms for loading software which | |
| follow the hardware mechanisms provided by the real hardware: | |
| - Magtape bootstraps toggled in through the front panel | |
| - Autoload mechanism for disk drives | |
| 3.1 Magtape bootstraps | |
| Software may be loaded from a magtape drive by using the SIMH command | |
| "boot mtx" (currently only drive 0 is supported) which loads an appropriate | |
| bootstrap into memory. This bootstrap loads the next record from the tape and | |
| starts execution of the loaded code. | |
| 3.1.1 Default bootstrap | |
| The default bootstrap is used for loading operating system distribution | |
| tapes and is loaded at location 0. Register A is set according to the amount | |
| os memory installed in the system: | |
| - 0x5000 if 32KW or greater is installed | |
| - 0x4000 if 24KW or 28KW is installed | |
| - 0x2000 if less than 24KW is installed | |
| 3.1.2 SMM17 bootstrap | |
| SMM17 is the System Maintenance Monitor and uses a tailored bootstrap | |
| which is loaded into the highest addressed 4KW module installed in the system. | |
| The following switches may be used with the "boot" command for special | |
| handling: | |
| -S load the SMM17 bootstrap rather than the default bootstrap | |
| -D configure the SMM17 bootstrap to use Buffered Data Channel #1 | |
| to access the magtape controller | |
| 3.2 Disk autoload | |
| The autoload mechanism loads track 0 from logical drive 0 of a disk or | |
| drum controller to memory location 0, it does not start execution of the loaded | |
| code (some of the diagnostics code relies on this). DP, CDD and DRM controllers | |
| support the autoload command ("autoload dp", "autoload cdd" or "autoload drm") | |
| which is normally followed by a "run 0" command to start execution of the | |
| loaded code. | |
| 4. Operating The Simulator | |
| 4.1 CPU | |
| The control panel of a physical CDC 1700 system has a number of | |
| switches which control the operation of the CPU. In the simulator, these | |
| switches can be turned on and off with the commands "set cpu xxx" and | |
| "set cpu noxxx". By default, all the switches are off. | |
| 4.1.1 Selective Stop (set cpu sstop/nosstop) | |
| The Selective Stop switch controls how the "Selective Stop (SLS)" | |
| instruction executes. If the switch is Off, SLS executes as a no-operation. | |
| If the switch is On, SLS executes as a halt instruction. Continuing after | |
| the halt causes the CPU to execute the instruction following SLS. | |
| 4.1.2 Selective Skip (set cpu sskip/nosskip) | |
| The Selective Skip switch controls how the SWS and SWN skip | |
| instruction execute. SWS will skip if the switch is set and SWN will skip if | |
| the switch is not set. Both the Selective Stop and Selective Skip switches | |
| are used extensively to control execution of the System Maintenance Monitor. | |
| 4.1.3 Protect (set cpu protect/noprotect) | |
| Each word of memory on the CDC 1700 series consists of 18-bits; 16-bits | |
| of data/instructions, a parity bit (which is not implemented in the simulator) | |
| and a program protect bit. If the Protect switch is Off, any program may | |
| reference any word of memory. If the Protect switch is On, there are a set of | |
| rules which control how memory accesses work and when to generate a program | |
| protect violation - see one of the 1700 reference manuals on bitsavers.org for | |
| exact details. | |
| The simulator fully implements CPU protect mode allowing protected | |
| operating systems such as MSOS 5 to execute. It does not support peripheral | |
| protect operation which allows unprotected programs to directly access | |
| some unprotected peripherals. | |
| Operating systems and other programs which run with the Protect | |
| switch on usually start up with the Protect switch off, manipulate the | |
| protect bits in memory (using the CPB/SPB instructions) and then ask the | |
| operator to set the Protect switch on. | |
| 4.2 Teletype | |
| The console teletype on some of the earlier models of the CDC 1700 | |
| series had a "Manual Interrupt" button so that the operator could get the | |
| attention of the operating system. Later models used a display terminal and | |
| used the "Control+G" key conbination to generate a Manual Interrupt. The | |
| Simulator follows this convention of using the "Control+G" key combination. | |
| The actual key combination may be changed by issuing the command | |
| "deposit tti intrkey xx" where xx is desired key code in hex. | |
| 5. Software | |
| There is some software available at bitsavers.org in the | |
| bits/CDC/1700_Cyber18 directory, see CDC1700-Diagnostics.txt and | |
| CDC1700-MSOS.txt for more details. | |
| 6. Cyber-18 | |
| The CDC 1700 later morphed into the Cyber-18 series. This series | |
| included an enhanced instruction set using unused bits from the 1700 | |
| instruction encoding. The simulator can detect these instructions and can be | |
| configured to stop if it tries to execute such an instruction | |
| (set cpu debug=enhanced). Due to a lack of detailed documentation it it | |
| unlikely that the enhanced instruction set will ever be completely implemented. |